ABSTRACT
We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν–log ν Fν representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, αro, and optical to X-ray, αox, spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (νSpeak) is positioned between 1012.5 and 1014.5 Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 1013 and 1017 Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron–inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked (HBL) BL Lacs are detected in the LBAS sample, only less than 13% of known bright FSRQs and LBL BL Lacs are included. This suggests that the latter sources, as a class, may be much fainter γ-ray emitters than LBAS blazars, and could in fact radiate close to the expectations of simple SSC models. We categorized all our sources according to a new physical classification scheme based on the generally accepted paradigm for Active Galactic Nuclei and on the results of this SED study. Since the LAT detector is more sensitive to flat spectrum γ-ray sources, the correlation between νSpeak and γ-ray spectral index strongly favors the detection of high energy peaked blazars, thus explaining the Fermi overabundance of this type of sources compared to radio and EGRET samples. This selection effect is similar to that experienced in the soft X-ray band where HBL BL Lacs are the dominant type of blazars.
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1. INTRODUCTION
The Large Area Telescope (LAT) on board the Fermi Gamma Ray Space Telescope, launched on 2008 June 11, provides unprecedented sensitivity in the γ-ray band (20 MeV to over 300 GeV; Atwood et al. 2009) with a large increase over its predecessors EGRET (Thompson et al. 1993), and AGILE, an Italian small γ-ray astronomy mission launched in 2007 (Tavani et al. 2008). The first three months of operations in the sky-survey mode led to the compilation of a list of 205 γ-ray sources with statistical significance larger than 10σ (Abdo et al. 2009a). As largely expected from the results of EGRET and AGILE, most of the high Galactic latitude sources in this catalog are blazars (Abdo et al. 2009b), a type of active galactic nucleus (AGN) well known to display extreme observational properties like large and rapid variability, apparent super-luminal motion, flat or inverted radio spectrum, and large and variable polarization. According to a widely accepted scenario, blazars are thought to be objects emitting non-thermal radiation across the entire electromagnetic spectrum from a relativistic jet that is viewed closely along the line of sight, thus causing strong relativistic amplification (e.g., Blandford & Rees 1978; Urry & Padovani 1995).
Blazars are rare extragalactic objects as they are a subset of radio loud quasi-stellar objects (QSOs), which in turn are only ≈10% of radio quiet QSOs and Seyfert galaxies that are found in large numbers at optical and at X-ray frequencies. Despite that, the strong emission at all wavelengths that characterizes blazars makes them the dominant type of extragalactic sources in those energy windows where the accretion onto a supermassive black hole, or other thermal mechanisms, do not produce significant radiation. For instance, in the microwave band, Giommi & Colafrancesco (2004) showed that blazars are the largest population of extragalactic objects (see also Toffolatti et al. 1998). The same is true in the γ-ray band (Hartman et al. 1999; Abdo et al. 2009b) and at TeV energies where BL Lac objects are the most frequent type of sources found in the high Galactic latitude sky (e.g., Costamante & Ghisellini 2002; Colafrancesco & Giommi 2006), see, e.g., the Web-based TeVCat92 catalog for an up-to-date list of TeV sources and Weekes (2008) for a recent review.
Blazars have been known and studied in different energy windows for over 40 years; however, many questions still remain open about their physics and demographics.
One of the most effective ways of studying the physical properties of blazars is through the use of multi-frequency data. This approach has been followed by a number of authors (e.g., Giommi et al. 1995; von Montigny et al. 1995; Sambruna et al. 1996; Fossati et al. 1998; Giommi et al. 2002; Nieppola et al. 2006; Padovani et al. 2006) who assembled the spectral energy distributions (SED) of many radio, X-ray, and γ-ray selected blazars. In all cases, however, the effectiveness of the method was limited by the availability of only sparse, often non-simultaneous, flux measurements covering a limited portion of the electromagnetic spectrum. The need to build simultaneous and detailed SED is usually addressed through the organization of specific multifrequency observation campaigns. However, so far these large efforts have been carried out almost exclusively on the occasion of large flaring events of a few bright and well-known blazars, e.g., 3C454.3 (Giommi et al. 2006; Abdo et al. 2010b; Vercellone et al. 2009), Mkn421 (Donnarumma et al. 2009), and PKS2155-304 (Aharonian et al. 2009).
With Fermi, Swift, and other high-energy astrophysics satellites simultaneously in orbit, complemented by other space and ground-based observatories, it is now possible to assemble high-quality data to build simultaneous and well-sampled SED of large and unbiased samples of AGNs.
In this paper, we study the broadband (radio to high-energy γ-ray) properties of the sample of Fermi bright blazars recently presented by Abdo et al. (2009b) and we derive the detailed SED of a subsample of 48 Fermi blazars using simultaneous or quasi-simultaneous data obtained from Swift and other ground- and space-based observatories. For the sake of brevity we will limit ourselves to presenting the data, to estimating some key parameters characterizing the SED, and to making some basic conclusions about the physics of blazars. Detailed fits, statistical studies, and more complete theoretical interpretations will be presented elsewhere. Full analysis of the LAT γ-ray spectra and γ-ray variability of all the LBAS sources is presented in dedicated papers (Abdo et al. 2010a, 2010b).
This paper is organized as follows. In Section 2, we present the sample; in Section 3, we describe the Fermi and Swift high energy data along with radio, near-infrared, optical, and other multi-frequency data. In Section 4, we build quasi-simultaneous SED for 48 LBAS AGNs. In Section 5, we use our SED to derive some key physical parameters such as the peak frequency of the synchrotron and inverse Compton power (νSpeak and νICpeak) and the corresponding peak fluxes. We also describe an empirical method that can be used for approximating the synchrotron bump parameters from simple observational quantities such as αox and αro. We then calculate physical parameters for all sources in the LBAS sample for which αox and αro are available from data in the literature. In Section 6, we derive a new physical classification of AGNs based on our findings and we categorize all our blazars accordingly. In Section 7, we discuss some physical implications of our findings. Finally, in Section 8 we summarize and discuss our results.
2. THE SAMPLE
The results of the first three months of operations of the Fermi γ-ray observatory, from 2008 August 4 to October 31, are described in Abdo et al. (2009a), who presented a list of 205 bright (>10σ) γ-ray sources. In a companion publication Abdo et al. (2009b) studied the AGN content of this list associating with high confidence 106 sources at |b|>10° with AGNs; ten further sources were also associated with AGNs but with a lower degree of confidence. This sample has been named the "LAT Bright AGN Sample" or LBAS. The results of the Abdo et al. (2009b) paper that are most relevant for this work are as follows.
- 1.About 90% of the LBAS sources have been associated with AGNs listed in radio catalogs (CRATES/CGRaBS, BZCat), thus implying that the bright extragalactic γ-ray sky is confirmed to be dominated by radio-loud AGNs (flat spectrum radio quasars, FSRQs, BL Lacs, and radio galaxies).
- 2.The number of high-energy peaked (HBL) BL Lacs detected at GeV energies (even when not flaring) has risen to at least 10 (out of 42 BL Lacs) as compared to only one (out of 14 BL Lacs) detected by EGRET. Seven LBAS BL Lacs are known TeV blazars.
- 3.Only about one-third of the bright Fermi AGN were also detected by EGRET. This is a likely consequence of the strong variability and duty cycle of GeV blazars.
- 4.BL Lac objects make up almost half of the bright Fermi AGN sample, which consists of 58 FSRQs, 42 BL Lac objects, two radio galaxies, and four AGNs of unknown type; the BL Lac fraction in the 3EG catalog was only ∼23%. This is probably the result of a selection effect induced by the different response of the EGRET and LAT instruments.
- 5.HBL BL Lacs show significantly harder spectra than FSRQs and low energy peaked (LBL) BL Lacs.
Our purpose here is to study in detail the broadband spectral properties of all blazars in the LBAS sample. The main properties of our sources are reported in Table 1. Column 1 gives the γ-ray source name as it appears in Abdo et al. (2009a); Column 2 gives the name(s) of the blazar associated with the γ-ray source; Columns 3 and 4 give the precise equatorial coordinates taken from the BZCat catalog (Massaro et al. 2009) or from NED; Column 5 gives the redshift (when known); Columns 6 and 7 give the 5 GHz radio flux density and the optical apparent magnitude, Vmag, from the CRATES (Healey et al. 2007) and from the USNO-B1 (Monet et al. 2003) catalogs respectively; Column 8 gives the 0.1–2.4 keV X-ray flux from the BZcat, or from recent Swift observations processed at the ASI Science Data Center (ASDC), as described in Section 3.2.4. All fluxes are as observed, that is, not corrected for Galactic absorption. Finally, Columns 9, 10, and 11 give the broadband (rest-frame) spectral slopes between 5 GHz and 5000 Å (αro), 5000 Å and 1 keV (αox), 5 GHz and 1 keV (αrx), and 1 keV and 100 MeV (αxγ) respectively, with αab defined as
where fa is the rest-frame flux at frequency νa properly de-reddened for Galaxy absorption. The flux measurements and the redshifts used for the calculation of αro, αox, αrx, and αxγ are from Table 1 of this paper and from Table 3 of Abdo et al. (2009b). For the case of BL Lac objects without known redshift we have assumed z = 0.4.
Table 1. Sources List and Basic Parameters
LAT Name | Counterpart Name(s) | R.A. | Decl. | Z | Radio Flux | Vmag | X-ray Flux a | αro | αox | αrx | αxγ |
---|---|---|---|---|---|---|---|---|---|---|---|
0FGL | (J2000.0) | (J2000.0) | (6 cm, mJy) | (erg cm−2 s−1) | |||||||
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) | (11) | (12) |
J0017.4 − 0503 | 1RXS J001736.1-0/BZQJ0017-0512 | 00 17 35.8 | −05 12 41.6 | 0.227 | 274 | 18.2 | 8.03e-13 | 0.59 | 1.28 | 0.83 | 0.57 |
J0033.6 − 1921 | 1RXS J003334.6-1/BZBJ0033-1921 | 00 33 34.3 | −19 21 33.6 | 0.61 | ... | 16.1 | 8.43e-12 | 0.23 | 1.08 | 0.53 | 1.04 |
J0050.5 − 0928 | PKS0048-09/BZBJ0050-0929 | 00 50 41.2 | −09 29 05.2 | ... | 931 | 17.3 | 2.33e-12 | 0.52 | 1.46 | 0.84 | 0.72 |
J0051.1 − 0647 | PKS0048-71/BZQJ0051-0650 | 00 51 08.2 | −06 50 02.1 | 1.975 | 841 | 20.1 | 4.18e-13 | 0.85 | 1.02 | 0.93 | 0.59 |
J0100.2+0750 | GB6J0100+0745 | 01 00 20.8 | +07 45 50.4 | ... | 101 | ... | ... | ... | ... | ... | 0 |
J0112.1+2247 | GC 0109+224/BZBJ0112+2244 | 01 12 05.8 | +22 44 38.7 | ... | 304 | 15.3 | 1.93e-12 | 0.33 | 1.67 | 0.79 | 0.74 |
J0118.7 − 2139 | PKS 0116-219/BZQJ0118-2141 | 01 18 57.1 | −21 41 30.0 | 1.165 | 559 | 20 | 1.42e-13 | 0.79 | 1.23 | 0.97 | 0.47 |
J0120.5 − 2703 | 1Jy0118-272/BZBJ0120-2701 | 01 20 31.6 | −27 01 24.7 | 0.557 | 1000 | 16.5 | 7.22e-13 | 0.49 | 1.66 | 0.91 | 0.74 |
J0136.6+3903 | 1RXS J013632.9+3/BZBJ0136+3905 | 01 36 32.4 | +39 05 59.3 | ... | 49 | 15.4 | 9.6e-12 | 0.24 | 1.28 | 0.59 | 1.04 |
J0137.1+4751 | S40133+47/BZQJ0136+4751 | 01 36 58.4 | +47 51 29.0 | 0.859 | 2016 | 16.7 | 1.04e-12 | 0.71 | 1.25 | 0.93 | 0.64 |
J0144.5+2709 | CLASSJ0144+2705 | 01 44 33.4 | +27 05 03.0 | ... | 263 | 19.6 | ... | 0.71 | ... | ... | 0 |
J0145.1 − 2728 | PKS 0142-278/BZQJ0145-2733 | 01 45 03.2 | −27 33 34.3 | 1.148 | 833 | 18.4 | 5e-13 | 0.7 | 1.3 | 0.92 | 0.57 |
J0204.8 − 1704 | PKS 0202-17/BZQJ0204-1701 | 02 04 57.5 | −17 01 18.8 | 1.74 | 1350 | 18.5 | 5.66e-13 | 0.71 | 1.3 | 0.94 | 0.57 |
J0210.8 − 5100 | PKS0208-512/BZUJ0210-5101 | 02 10 46.1 | −51 01 01.8 | 1.003 | 3198 | 16.9 | 7.51e-13 | 0.59 | 1.66 | 0.97 | 0.54 |
J0217.8+0146 | PKS 0215+015/BZQJ0217+0144 | 02 17 48.9 | +01 44 49.7 | 1.715 | 1419 | 19.4 | 1.17e-12 | 0.79 | 0.96 | 0.9 | 0.67 |
J0220.9+3607 | 1Jy0218+357/BZUJ0221+3556 | 02 21 05.5 | +35 56 13.9 | 0.944 | 1480 | 20 | 3.97e-13 | 0.94 | 0.99 | 0.97 | 0.53 |
J0222.6+4302 | 3C 66A/BZBJ0222+4302 | 02 22 39.6 | +43 02 07.7 | 0.444 | 988 | 14.4 | 2.29e-12 | 0.41 | 1.68 | 0.84 | 0.66 |
J0229.5 − 3640 | PKS0227-369/BZQJ0229-3643 | 02 29 28.3 | −36 43 56.7 | 2.115 | 149 | 18.6 | 5.33e-13 | 0.76 | 0.82 | 0.82 | 0.53 |
J0238.4+2855 | 4C28.07/BZQJ0237+2848 | 02 37 52.3 | +28 48 08.9 | 1.213 | 2794 | 17.8 | 5.77e-13 | 0.86 | 1.13 | 0.98 | 0.59 |
J0238.6+1636 | PKS0235+164/BZBJ0238+1636 | 02 38 38.8 | +16 36 59.2 | 0.94 | 1935 | 18.1 | 1.24e-12 | 0.75 | 1.15 | 0.92 | 0.51 |
J0245.6 − 4656 | PKS0244-470 | 02 45 59.8 | −46 51 17.1 | ... | 852 | 18.2 | 7.71e-13 | 0.74 | 1.21 | 0.9 | 0.66 |
J0303.7 − 2410 | PKS 0301-243/BZBJ0303-2407 | 03 03 26.5 | −24 07 13.0 | 0.26 | 397 | 15.8 | 5.78e-12 | 0.43 | 1.33 | 0.74 | 0.9 |
J0334.1 − 4006 | PKS0332-403/BZBJ0334-4008 | 03 34 13.6 | −40 08 25.4 | ... | 1331 | 16.7 | 7.34e-13 | 0.71 | 1.34 | 0.93 | 0.68 |
J0349.8 − 2102 | PKS 0347-211/BZQJ0349-2102 | 03 49 57.7 | −21 02 47.6 | 2.944 | 403 | 21.1 | 4.07e-13 | 0.76 | 0.98 | 0.89 | 0.49 |
J0407.6 − 3829 | PKS0405-385/BZUJ0406-3826 | 04 06 58.9 | −38 26 27.9 | 1.285 | 830 | 18.4 | 3.06e-13 | 0.62 | 1.46 | 0.95 | 0.56 |
J0412.9 − 5341 | SUMSSJ041313-533 | 04 13 13.3 | −53 31 58.6 | ... | 95 | 19.7 | ... | 0.59 | ... | ... | 0 |
J0423.1 − 0112 | PKS0420-01/BZQJ0423-0120 | 04 23 15.7 | −01 20 33.1 | 0.916 | 4357 | 15.1 | 1.39e-12 | 0.73 | 1.31 | 0.96 | 0.68 |
J0428.7 − 3755 | PKS0426-380/BZBJ0428-3756 | 04 28 40.3 | −37 56 19.6 | 1.03 | 1202 | 18 | 4.23e-13 | 0.54 | 1.61 | 0.95 | 0.5 |
J0449.7 − 4348 | PKS0447-439/BZBJ0449-4350 | 04 49 24.7 | −43 50 08.9 | 0.205 | 242 | 15.3 | 8.12e-12 | 0.35 | 1.35 | 0.69 | 0.83 |
J0457.1 − 2325 | PKS0454-234/BZQJ0457-2324 | 04 57 03.1 | −23 24 51.9 | 1.003 | 1863 | 17.9 | 4.68e-13 | 0.79 | 1.26 | 0.97 | 0.46 |
J0507.9+6739 | 1ES0502+675/BZBJ0507+6737 | 05 07 56.2 | +67 37 24.3 | 0.416 | 27 | 17.7 | 1.29e-11 | 0.3 | 0.97 | 0.54 | 1.07 |
J0516.2 − 6200 | MC4 0516-621/BZUJ0516-6207 | 05 16 44.8 | −62 07 05.4 | ... | 564 | 17.6 | 4.95e-13 | 0.78 | 1.14 | 0.9 | 0.64 |
J0531.0+1331 | PKS 0528+134/BZQJ0530+1331 | 05 30 56.3 | +13 31 55.2 | 2.07 | 3043 | 19.6 | 7.97e-13 | 0.75 | 1.2 | 0.97 | 0.53 |
J0538.8 − 4403 | PKS0537-441/BZBJ0538-4405 | 05 38 50.2 | −44 05 08.9 | 0.892 | 4805 | 15.2 | 2.1e-12 | 0.64 | 1.41 | 0.94 | 0.6 |
J0654.3+5042 | GB6J0654+5042 | 06 54 22.0 | +50 42 21.0 | ... | 136 | 15.6 | ... | 0.33 | ... | ... | 0 |
J0654.3+4513 | S4 0650+45/BZUJ0654+4514 | 06 54 23.6 | +45 14 23.4 | 0.933 | 467 | 18.9 | 2.38e-13 | 0.79 | 1.14 | 0.93 | 0.44 |
J0700.0 − 6611 | PKS0700-661 | 07 00 31.0 | −66 10 44.2 | ... | 245 | 14.8 | 3.53e-13 | 0.31 | 1.96 | 0.87 | 0.66 |
J0712.9+5034 | BZBJ0712+5033 | 07 12 43.6 | +50 33 22.7 | ... | 127 | 19.3 | 2.48e-13 | 0.55 | 1.45 | 0.85 | 0.62 |
J0714.2+1934 | 87GB071100.0+194 | 07 13 55.6 | +19 35 03.9 | ... | 116 | 18.6 | ... | 0.55 | ... | ... | 0 |
J0719.4+3302 | GB2 0716+332/BZUJ0719+3307 | 07 19 19.3 | +33 07 09.6 | 0.779 | 321 | 16.3 | 2.51e-13 | 0.64 | 1.35 | 0.91 | 0.54 |
J0722.0+7120 | S50716+714/BZBJ0721+7120 | 07 21 53.4 | +71 20 36.3 | ... | 859 | 14.6 | 2.27e-12 | 0.39 | 1.71 | 0.84 | 0.69 |
J0730.4 − 1142 | PKS0727-11/BZQJ0730-1141 | 07 30 19.0 | −11 41 12.5 | 1.589 | 5771 | ... | 4.68e-13 | 0.87 | 1.19 | 1.03 | 0.48 |
J0738.2+1738 | PKS0735+17/BZBJ0738+1742 | 07 38 07.3 | +17 42 19.0 | 0.424 | 1812 | 15.7 | 9.67e-13 | 0.47 | 1.78 | 0.93 | 0.72 |
J0818.3+4222 | S4 0814+425/BZBJ0818+4222 | 08 18 16.0 | +42 22 45.4 | 0.53 | 1866 | 18.6 | 3.23e-13 | 0.88 | 1.11 | 0.99 | 0.56 |
J0824.9+5551 | OJ 535/BZQJ0824+5552 | 08 24 47.2 | +55 52 42.7 | 1.417 | 1155 | 17.3 | 6.4e-13 | 0.77 | 1.18 | 0.93 | 0.56 |
J0855.4+2009 | PKS0851+202/BZBJ0854+2006 | 08 54 48.7 | +20 06 30.5 | 0.306 | 2908 | 15.4 | 1.72e-12 | 0.49 | 1.69 | 0.92 | 0.7 |
J0909.7+0145 | PKS0907+022/BZBJ0909+0200 | 09 09 39.7 | +02 00 05.2 | ... | 218 | 18.3 | ... | 0.68 | ... | ... | 0 |
J0921.2+4437 | S40917+44/BZQJ0920+4441 | 09 20 58.3 | +44 41 53.9 | 2.19 | 1085 | 16.6 | 1.04e-12 | 0.85 | 0.89 | 0.89 | 0.65 |
J0948.3+0019 | 1RXS J094856.9+0/BZQJ0948+0022 | 09 48 57.3 | +00 22 25.6 | 0.585 | 295 | 17.7 | 5.24e-13 | 0.56 | 1.33 | 0.86 | 0.55 |
J0957.6+5522 | 4C55.17/BZQJ0957+5522 | 09 57 38.1 | +55 22 57.7 | 0.896 | 2015 | 17.4 | 5.13e-13 | 0.73 | 1.41 | 0.97 | 0.62 |
J1012.9+2435 | B2 1011+25/BZQJ1013+2449 | 10 12 41.2 | +24 39 21.7 | 1.805 | 94 | 19.3 | 6.24e-13 | 0.38 | 1.51 | 0.79 | 0.65 |
J1015.2+4927 | 1H 1013+498/BZBJ1015+4926 | 10 15 04.0 | +49 26 00.7 | 0.2 | 299 | 14.8 | 1.32e-11 | 0.38 | 1.23 | 0.68 | 0.98 |
J1015.9+0515 | SDSSJ101603.13+0/BZQJ1016+0513 | 10 16 03.1 | +05 13 02.3 | 1.713 | 593 | 19.9 | ... | 0.84 | ... | ... | 0 |
J1034.0+6051 | S4 1030+61/BZQJ1033+6051 | 10 33 51.4 | +60 51 07.3 | 1.401 | 532 | 19.5 | 3.19e-13 | 0.82 | 1.03 | 0.92 | 0.54 |
J1053.7+4926 | WE 1050+49W1/BZBJ1053+4929 | 10 53 44.0 | +49 29 56.0 | 0.14 | 59 | 15.1 | 8.21e-13 | 0.14 | 1.9 | 0.74 | 0.98 |
J1054.5+2212 | SDSSJ105430.62+2/BZBJ1054+2210 | 10 54 30.7 | +22 10 55.3 | ... | 55 | 18.8 | 2.55e-13 | 0.4 | 1.59 | 0.81 | 0.59 |
J1058.9+5629 | RXJ10586+5628/BZBJ1058+5628 | 10 58 37.6 | +56 28 11.2 | 0.143 | 247 | 15.4 | 3.13e-12 | 0.28 | 1.65 | 0.75 | 0.84 |
J1057.8+0138 | 4C01.28/BZUJ1058+0133 | 10 58 29.5 | +01 33 58.7 | 0.888 | 3403 | 17.5 | 1.08e-12 | 0.75 | 1.27 | 0.96 | 0.72 |
J1100.2 − 8000 | PKS1057-79/BZUJ1058-8003 | 10 58 43.3 | −80 03 54.2 | ... | 2130 | 18.5 | 4.34e-13 | 0.7 | 1.52 | 0.98 | 0.5 |
J1104.5+3811 | MKN421/BZBJ1104+3812 | 11 04 27.3 | +38 12 31.7 | 0.03 | 723 | 8.6 | 1.81e-10 | −0.08 | 1.86 | 0.58 | 1.1 |
J1129.8 − 1443 | PKS1127-145/BZQJ1130-1449 | 11 30 07.0 | −14 49 27.4 | 1.184 | 4209 | 16.1 | 1.39e-12 | 0.72 | 1.37 | 0.95 | 0.65 |
J1146.7 − 3808 | PKS1144-379/BZUJ1147-3812 | 11 47 01.3 | −38 12 11.0 | 1.048 | 1825 | 16.7 | 9.06e-13 | 0.6 | 1.53 | 0.93 | 0.69 |
J1159.2+2912 | 4C29.45/BZQJ1159+2914 | 11 59 31.7 | +29 14 44.8 | 0.729 | 1461 | 17 | 8.44e-13 | 0.67 | 1.4 | 0.92 | 0.61 |
J1218.0+3006 | ON 325/BZBJ1217+3007 | 12 17 52.0 | +30 07 00.5 | 0.13 | 478 | 13.7 | 2.49e-11 | 0.38 | 1.21 | 0.67 | 0.96 |
J1221.7+2814 | ON 231/BZBJ1221+2813 | 12 21 31.6 | +28 13 58.5 | 0.102 | 1085 | 14.1 | 1.3e-12 | 0.23 | 2.14 | 0.88 | 0.71 |
J1229.1+0202 | 3C273/BZQJ1229+0203 | 12 29 06.7 | +02 03 08.6 | 0.158 | 43572 | 13.2 | 6.31e-11 | 0.76 | 1.09 | 0.87 | 0.8 |
J1246.6 − 2544 | PKS1244-255/BZQJ1246-2547 | 12 46 46.7 | −25 47 49.3 | 0.635 | 2317 | 17.3 | 1.3e-12 | 0.67 | 1.33 | 0.92 | 0.7 |
J1248.7+5811 | PG 1246+586/BZBJ1248+5820 | 12 48 18.7 | +58 20 28.7 | ... | 356 | 15.9 | 3.99e-12 | 0.35 | 1.55 | 0.76 | 0.87 |
J1253.4+5300 | 1RXS J125311.9+5/BZBJ1253+5301 | 12 53 11.8 | +53 01 11.7 | ... | 363 | 16.3 | 2.7e-13 | 0.5 | 1.7 | 0.91 | 0.6 |
J1256.1 − 0548 | 3C279/BZQJ1256-0547 | 12 56 11.0 | −05 47 21.5 | 0.536 | 11192 | 16.9 | 2.09e-11 | 0.71 | 1.1 | 0.86 | 0.8 |
J1310.6+3220 | 1Jy1308+326/BZUJ1310+3220 | 13 10 28.6 | +32 20 43.8 | 0.997 | 1447 | 19.9 | 5.28e-13 | 0.92 | 0.97 | 0.95 | 0.55 |
J1331.7 − 0506 | PKS 1329-049/BZQJ1332-0509 | 13 32 04.3 | −05 09 43.3 | 2.15 | 471 | 17.6 | 3e-13 | 0.72 | 1.22 | 0.92 | 0.5 |
J1333.3+5058 | CLASSJ1333+5057 | 13 33 53.8 | +50 57 35.7 | 1.362 | 51 | 20.6 | ... | 0.71 | ... | ... | 0 |
J1355.0 − 1044 | PKS1352-104/BZUJ1354-1041 | 13 54 46.4 | −10 41 02.6 | 0.33 | 686 | 16.5 | 1.88e-12 | 0.6 | 1.27 | 0.84 | 0.72 |
J1427.1+2347 | PG 1424+240/BZBJ1427+2348 | 14 27 00.3 | +23 48 00.0 | ... | 335 | 15 | 3.57e-12 | 0.34 | 1.57 | 0.76 | 0.84 |
J1457.6 − 3538 | PKS1454-354/BZQJ1457-3539 | 14 57 26.7 | −35 39 10.0 | 1.424 | 566 | 17.3 | 5.1e-13 | 0.77 | 1.09 | 0.9 | 0.47 |
J1504.4+1030 | PKS1502+106/BZQJ1504+1029 | 15 04 24.9 | +10 29 39.1 | 1.839 | 2325 | 18.8 | 1.6e-13 | 0.92 | 1.16 | 1.04 | 0.31 |
J1511.2 − 0536 | 4C-05.64/BZQJ1510-0543 | 15 10 53.5 | −05 43 07.3 | 1.191 | 1742 | 16.6 | 4.56e-13 | 0.73 | 1.45 | 0.97 | 0.58 |
J1512.7 − 0905 | PKS1510-08/BZQJ1512-0905 | 15 12 50.5 | −09 05 59.7 | 0.36 | ... | 16.2 | 1.15e-12 | 0.61 | 1.54 | 0.93 | 0.49 |
J1517.9 − 2423 | APLIB/BZBJ1517-2422 | 15 17 41.8 | −24 22 19.4 | 0.048 | 2013 | 10.9 | 1.05e-12 | 0.33 | 2.09 | 0.93 | 0.75 |
J1522.2+3143 | B2 1520+31/BZQJ1522+3144 | 15 22 09.8 | +31 44 14.3 | 1.487 | 302 | 20 | 1.77e-13 | 0.8 | 1.1 | 0.92 | 0.4 |
J1543.1+6130 | 1RXS J154256.6+6/BZBJ1542+6129 | 15 42 56.8 | +61 29 55.2 | ... | 121 | 15.8 | 5.17e-13 | 0.43 | 1.56 | 0.81 | 0.73 |
J1553.4+1255 | PKS1551+130/BZQJ1553+1256 | 15 53 32.5 | +12 56 51.6 | 1.29 | 742 | 17.2 | ... | 0.66 | ... | ... | 0 |
J1555.8+1110 | PG 1553+113/BZBJ1555+1111 | 15 55 43.0 | +11 11 24.3 | ... | 510 | 13.8 | 1.79e-11 | 0.34 | 1.39 | 0.69 | 0.97 |
J1625.8 − 2527 | OS-237.8/BZUJ1625-2527 | 16 25 46.7 | −25 27 38.3 | 0.786 | 3449 | 20.5 | 9.34e-14 | 0.99 | 1.23 | 1.1 | 0.39 |
J1625.9 − 2423 | PMNJ1626-2426 | 16 26 59.7 | −24 26 41.8 | ... | 132 | ... | ... | ... | ... | ... | 0 |
J1635.2+3809 | 4C38.41/BZQJ1635+3808 | 16 35 15.4 | +38 08 04.4 | 1.814 | 3221 | 17.4 | 1.68e-13 | 0.78 | 1.49 | 1.06 | 0.41 |
J1641.4+3939 | NRAO512/BZQJ1640+3946 | 16 40 29.5 | +39 46 44.2 | 1.66 | 1117 | 18.5 | 3.46e-13 | 0.81 | 1.15 | 0.96 | 0.52 |
J1653.9+3946 | MKR501/BZBJ1653+3945 | 16 53 52.2 | +39 45 36.6 | 0.033 | 1375 | 9.2 | 3.69e-11 | −0.03 | 2.13 | 0.71 | 1.11 |
J1719.3+1746 | PKS 1717+177/BZBJ1719+1745 | 17 19 13.0 | +17 45 06.4 | 0.137 | 559 | 17.5 | 3.57e-13 | 0.62 | 1.47 | 0.92 | 0.62 |
J1751.5+0935 | OT 081/BZBJ1751+0939 | 17 51 32.8 | +09 39 00.6 | 0.322 | 2455 | 16.6 | 1.18e-12 | 0.65 | 1.4 | 0.93 | 0.6 |
J1802.2+7827 | S51803+784/BZBJ1800+7828 | 18 00 45.6 | +78 28 04.0 | 0.68 | 2633 | 16 | 7.9e-13 | 0.6 | 1.57 | 0.96 | 0.67 |
J1847.8+3223 | B21846+32A/BZQJ1848+3219 | 18 48 22.0 | +32 19 02.6 | 0.798 | 762 | 18.3 | 1e-12 | 0.75 | 1.04 | 0.88 | 0.6 |
J1849.4+6706 | 4C66.20/BZQJ1849+6705 | 18 49 16.0 | +67 05 41.7 | 0.657 | 845 | 17.5 | 4.07e-13 | 0.66 | 1.39 | 0.93 | 0.53 |
J1911.2 − 2011 | 1908-201/BZQJ1911-2006 | 19 11 09.5 | −20 06 55.1 | 1.119 | 2053 | 17.6 | 1.77e-12 | 0.85 | 0.97 | 0.9 | 0.61 |
J1923.3 − 2101 | PMNJ1923-2104/BZQJ1923-2104 | 19 23 32.1 | −21 04 33.3 | 0.874 | 2885 | 14.9 | 7.67e-13 | 0.71 | 1.43 | 0.97 | 0.59 |
J2000.2+6506 | 1ES1959+650/BZBJ1959+6508 | 19 59 59.8 | +65 08 54.7 | 0.047 | 238 | 12 | 3.53e-11 | 0.08 | 1.64 | 0.61 | 1.06 |
J2009.4 − 4850 | 1Jy2005-489/BZBJ2009-4849 | 20 09 25.3 | −48 49 53.6 | 0.071 | 1192 | 10.6 | 3.32e-11 | 0.16 | 1.75 | 0.7 | 1.09 |
J2017.2+0602 | CLASSJ2017+0603 | 20 17 13.3 | +06 03 06.5 | ... | 36 | 17.7 | 6.48e-14 | 0.35 | 1.85 | 0.86 | 0.53 |
J2025.6 − 0736 | 2022-077/BZQJ2025-0735 | 20 25 40.6 | −07 35 52.6 | 1.388 | 879 | 17.6 | 6.29e-13 | 0.81 | 1.09 | 0.91 | 0.46 |
J2056.1 − 4715 | PKS2052-47/BZQJ2056-4714 | 20 56 16.3 | −47 14 47.6 | 1.491 | 2026 | 17.9 | 5.86e-13 | 0.82 | 1.16 | 0.96 | 0.57 |
J2139.4 − 4238 | MH 2136-428/BZBJ2139-4239 | 21 39 24.1 | −42 35 20.3 | ... | 108 | 16.5 | 7.3e-13 | 0.34 | 1.64 | 0.78 | 0.66 |
J2143.2+1741 | S32141+17/BZQJ2143+1743 | 21 43 35.5 | +17 43 48.7 | 0.213 | 1006 | 15.1 | 6.3e-13 | 0.43 | 1.85 | 0.92 | 0.56 |
J2147.1+0931 | 1Jy2144+092/BZQJ2147+0929 | 21 47 10.0 | +09 29 46.7 | 1.113 | 1233 | 17.7 | 5.95e-13 | 0.66 | 1.39 | 0.93 | 0.54 |
J2157.5+3125 | B2 2155+31/BZQJ2157+3127 | 21 57 28.8 | +31 27 01.4 | 1.486 | 452 | 20.4 | 2.44e-13 | 0.8 | 1.09 | 0.93 | 0.54 |
J2158.8 − 3014 | PKS 2155-304/BZBJ2158-3013 | 21 58 52.0 | −30 13 32.0 | 0.116 | 407 | 11.9 | 3.25e-10 | 0.22 | 1.07 | 0.51 | 1.13 |
J2202.4+4217 | BLLAC/BZBJ2202+4216 | 22 02 43.2 | +42 16 40.0 | 0.069 | 2940 | 14.9 | 1.58e-12 | 0.29 | 2.17 | 0.93 | 0.7 |
J2203.2+1731 | PKS2201+171/BZQJ2203+1725 | 22 03 26.8 | +17 25 48.2 | 1.076 | 834 | 13.2 | 4.61e-13 | 0.81 | 1.06 | 0.93 | 0.61 |
J2207.0 − 5347 | PKS2204-54/BZQJ2207-5346 | 22 07 43.6 | −53 46 33.8 | 1.215 | 1410 | 17.8 | 5.22e-13 | 0.8 | 1.19 | 0.95 | 0.55 |
J2229.8 − 0829 | PKS2227-08/BZQJ2229-0832 | 22 29 40.0 | −08 32 54.3 | 1.56 | 2423 | 18 | 3.74e-12 | 0.66 | 1.08 | 0.87 | 0.69 |
J2232.4+1141 | 4C-11.69/BZQJ2232+1143 | 22 32 36.4 | +11 43 50.9 | 1.037 | 3967 | 16.5 | 1.26e-12 | 0.77 | 1.32 | 0.96 | 0.61 |
J2254.0+1609 | 3C454.3/BZQJ2253+1608 | 22 53 57.7 | +16 08 53.5 | 0.859 | 14468 | 15.8 | 7.8e-12 | 0.58 | 1.55 | 0.93 | 0.53 |
J2325.3+3959 | BZBJ2325+3957 | 23 25 17.8 | +39 57 37.0 | ... | 135 | 20.3 | 1.02e-13 | 0.5 | 1.7 | 0.91 | 0.59 |
J2327.3+0947 | PKS2325+093/BZQJ2327+0940 | 23 27 33.4 | +09 40 09.5 | 1.843 | 643 | 18.1 | 7.27e-13 | 0.77 | 1.04 | 0.89 | 0.54 |
J2345.5 − 1559 | PMN 2345-1555/BZQJ2345-1555 | 23 45 12.4 | −15 55 07.7 | 0.621 | 504 | 18.6 | 2.6e-13 | 0.7 | 1.28 | 0.93 | 0.51 |
3. MULTI-FREQUENCY OBSERVATIONS
In this section, we describe the multi-frequency observations of LBAS blazars carried out between 2008 August and October with Fermi, and between 2008 May and 2009 January with Swift and other space and ground-based facilities.
3.1. Fermi-LAT Data Analysis and γ-ray Energy Spectra
The LAT γ-ray spectra of all the LBAS sources are studied in detail in a dedicated paper (Abdo et al. 2010a) based on 6 months of Fermi data. Here we derive the detailed γ-ray spectra of the 48 blazars for which we build the quasi-simultaneous SED based on the three months of data used to define the LBAS sample.
The Fermi-LAT data from 2008 August 4 to October 31 have been analyzed, selecting for each source only photons belonging to the diffuse class (Pass6 V3 IRF; Atwood et al. 2009). Events within a 15° region of interest (RoI) centered around the source have been selected. In order to discard photons from the Earth albedo, events with zenith angles larger than 105° with respect to the Earth reference frame (Abdo et al. 2009a) have been excluded from the data samples.
A maximum likelihood analysis (gtlike)93 has been used to reconstruct the source energy spectrum. A model is assumed for the source spectrum as well as for the diffuse background components, depending on a set of free parameters. The Galactic diffuse emission is modeled using the GALPROP package while the extragalactic one is described by a simple power law (Abdo et al. 2009a). The method has been implemented to estimate the parameters in each individual energy bin (two bins per decade, starting from 100 MeV), and the parameters obtained from the fits are used to evaluate the sources fluxes. For each energy bin the source under investigation and all nearby sources in the RoI are described by one parameter representing the integral flux in that energy bin. The diffuse background components are modeled with one single parameter each, describing the normalization. For each bin, only fit results with a significance larger than 3σ have been retained. Depending on the flux and energy spectrum, 4–7 bins had positive detections for each AGN in the sample. The results are shown in Table 2.
Table 2. Results of Fermi-LAT Data Analysis (Flux in Units of photons MeV−1 cm−2 s−1)
LAT Name | Band 1 | Band 2 | Band 3 | Band 4 | Band 5 | Band 6 | Band 7 |
---|---|---|---|---|---|---|---|
0FGL | 100–316.2 MeV | 316.2–1000 MeV | 1000–3162.3 MeV | 3162.3–10000 MeV | 10000–31623 MeV | 31623–100000 MeV | 100000–316230 MeV |
J0033.6 − 1921 | ... | (4.45 ± 1.06) 10−12 | (1.23 ± 0.28) 10−12 | (1.16 ± 0.47) 10−13 | (1.67 ± 0.96) 10−14 | ... | ... |
J0050.5 − 0928 | (3.83 ± 0.64) 10−10 | (3.83 ± 0.31) 10−11 | (3.04 ± 0.49) 10−12 | (2.02 ± 0.65) 10−13 | ... | ... | ... |
J0137.1+4751 | (3.33 ± 0.72) 10−10 | (3.14 ± 0.44) 10−11 | (3.29 ± 0.50) 10−12 | (2.64 ± 0.72) 10−13 | ... | ... | ... |
J0210.8 − 5100 | (9.20 ± 0.80) 10−10 | (7.23 ± 0.55) 10−11 | (5.99 ± 0.68) 10−12 | (2.87 ± 0.79) 10−13 | ... | ... | ... |
J0222.6+4302 | (9.70 ± 0.47) 10−10 | (9.89 ± 0.49) 10−11 | (8.77 ± 0.72) 10−12 | (9.26 ± 1.35) 10−13 | (1.16 ± 0.25) 10−13 | (1.47 ± 0.49) 10−14 | (6.57 ± 6.14) 10−16 |
J0229.5 − 3640 | (6.18 ± 0.68) 10−10 | (3.26 ± 0.40) 10−11 | (2.08 ± 0.42) 10−12 | (7.60 ± 4.00) 10−14 | ... | ... | ... |
J0238.4+2855 | (3.01 ± 0.65) 10−10 | (1.95 ± 0.37) 10−11 | (1.56 ± 0.38) 10−12 | (6.91 ± 4.04) 10−14 | ... | ... | ... |
J0238.6+1636 | (2.63 ± 0.11) 10−9 | (2.64 ± 0.09) 10−10 | (2.74 ± 0.13) 10−11 | (2.27 ± 0.20) 10−12 | (9.74 ± 2.27) 10−14 | (2.12 ± 2.04) 10−15 | ... |
J0349.8 − 2102 | (6.94 ± 0.71) 10−10 | (4.15 ± 0.32) 10−11 | (2.62 ± 0.47) 10−12 | (5.73 ± 3.74) 10−14 | ... | ... | ... |
J0423.1 − 0112 | (5.92 ± 0.77) 10−10 | (2.33 ± 0.24) 10−11 | (1.52 ± 0.30) 10−12 | (1.25 ± 0.53) 10−13 | ... | ... | ... |
J0428.7 − 3755 | (8.74 ± 0.78) 10−10 | (7.12 ± 0.43) 10−11 | (7.96 ± 0.76) 10−12 | (6.71 ± 1.18) 10−13 | (2.84 ± 1.28) 10−14 | ... | ... |
J0449.7 − 4348 | (4.31 ± 0.67) 10−10 | (3.38 ± 0.30) 10−11 | (4.60 ± 0.51) 10−12 | (4.02 ± 0.91) 10−13 | (4.10 ± 1.55) 10−14 | (2.55 ± 2.50) 10−15 | ... |
J0457.1 − 2325 | (1.46 ± 0.09) 10−9 | (1.27 ± 0.06) 10−10 | (1.11 ± 0.09) 10−11 | (6.54 ± 1.15) 10−13 | (2.78 ± 1.25) 10−14 | ... | ... |
J0507.9+6739 | (9.77 ± 6.47) 10−11 | (1.16 ± 0.34) 10−11 | (5.66e ± 2.66) 10−13 | (1.74 ± 0.58) 10−13 | (7.13 ± 6.55) 10−15 | (7.27 ± 3.43) 10−15 | (1.07 ± 0.76) 10−15 |
J0516.2 − 6200 | (3.41 ± 0.71) 10−10 | (1.68 ± 0.21) 10−11 | (1.79 ± 0.40) 10−12 | (1.06 ± 0.50) 10−13 | (8.93 ± 8.13) 10−15 | ... | ... |
J0531.0+1331 | (9.52 ± 1.05) 10−10 | (5.35 ± 0.63) 10−11 | (3.50 ± 0.58) 10−12 | (1.21 ± 0.56) 10−13 | ... | ... | ... |
J0538.8 − 4403 | (1.29 ± 0.09) 10−9 | (1.21 ± 0.06) 10−10 | (1.02 ± 0.09) 10−11 | (7.97 ± 1.30) 10−13 | (1.81 ± 1.05) 10−14 | (1.83 ± 1.82) 10−15 | ... |
J0712.9+5034 | (8.82 ± 6.15) 10−11 | (1.65 ± 0.35) 10−11 | (1.42 ± 0.36) 10−12 | (9.94 ± 4.70) 10−14 | ... | ... | ... |
J0722.0+7120 | (6.17 ± 0.72) 10−10 | (5.51 ± 0.46) 10−11 | (5.70 ± 0.60) 10−12 | (5.80 ± 1.00) 10−13 | (9.83 ± 7.05) 10−15 | ... | ... |
J0730.4 − 1142 | (1.25 ± 0.11) 10−9 | (8.46 ± 0.46) 10−11 | (7.43 ± 0.68) 10−12 | (3.33 ± 0.85) 10−13 | (3.85 ± 1.46) 10−14 | ... | ... |
J0855.4+2009 | (3.53 ± 0.64) 10−10 | (2.74 ± 0.38) 10−11 | (1.71 ± 0.39) 10−12 | (1.12 ± 0.50) 10−13 | ... | ... | ... |
J0921.2+4437 | (3.62 ± 0.59) 10−10 | (2.02 ± 0.22) 10−11 | (1.55 ± 0.37) 10−12 | (1.47 ± 0.52) 10−13 | (1.08 ± 0.77) 10−14 | ... | ... |
J1015.2+4927 | (2.72 ± 0.58) 10−10 | (1.69 ± 0.31) 10−11 | (3.25 ± 0.49) 10−12 | (3.85 ± 0.87) 10−13 | (4.66 ± 1.63) 10−14 | (3.33 ± 2.35) 10−15 | ... |
J1057.8+0138 | (2.73 ± 0.64) 10−10 | (1.13 ± 0.32) 10−11 | (1.44 ± 0.35) 10−12 | (9.10 ± 4.89) 10−14 | (8.84 ± 8.20) 10−15 | ... | ... |
J1058.9+5629 | (1.82 ± 0.58) 10−10 | (1.12 ± 0.16) 10−11 | (1.44 ± 0.29) 10−12 | (5.27 ± 3.30) 10−14 | ... | ... | ... |
J1104.5+3811 | (5.67 ± 0.65) 10−10 | (6.04 ± 0.38) 10−11 | (8.54 ± 0.72) 10−12 | (1.06 ± 0.14) 10−12 | (7.40 ± 2.03) 10−14 | (2.71 ± 0.68) 10−14 | (2.47 ± 1.23) 10−15 |
J1159.2+2912 | (4.41 ± 0.65) 10−10 | (2.70 ± 0.26) 10−11 | (1.14 ± 0.32) 10−12 | (9.05 ± 4.46) 10−14 | ... | ... | ... |
J1221.7+2814 | (2.66 ± 0.72) 10−10 | (3.20 ± 0.41) 10−11 | (4.07 ± 0.55) 10−12 | (2.78 ± 0.73) 10−13 | (2.68 ± 1.20) 10−14 | (3.72 ± 2.70) 10−15 | ... |
J1229.1+0202 | (2.92 ± 0.11) 10−9 | (1.45 ± 0.06) 10−10 | (7.70 ± 0.73) 10−12 | (1.13 ± 0.49) 10−13 | (5.36 ± 5.37) 10−15 | ... | ... |
J1248.7+5811 | (1.66 ± 0.57) 10−10 | (1.48 ± 0.27) 10−11 | (1.40 ± 0.34) 10−12 | (8.65 ± 4.11) 10−14 | (1.84 ± 1.02) 10−14 | (4.84 ± 2.81) 10−15 | ... |
J1256.1 − 0547 | (9.69 ± 0.83) 10−10 | (8.01 ± 0.44) 10−11 | (5.66 ± 0.59) 10−12 | (4.06 ± 0.87) 10−13 | (1.90 ± 1.05) 10−14 | ... | ... |
J1310.6+3220 | (6.42 ± 0.67) 10−10 | (4.66 ± 0.44) 10−11 | (3.76 ± 0.52) 10−12 | (3.29 ± 0.80) 10−13 | ... | ... | ... |
J1457.6 − 3538 | (1.21 ± 0.10) 10−9 | (1.24 ± 0.06) 10−10 | (8.42 ± 0.73) 10−12 | (5.07 ± 1.03) 10−13 | (2.45 ± 1.25) 10−14 | ... | ... |
J1504.4+1030 | (2.81 ± 0.11) 10−9 | (2.67 ± 0.08) 10−12 | (2.40 ± 0.12) 10−11 | (1.75 ± 0.18) 10−12 | (5.16 ± 1.64) 10−14 | (5.23 ± 2.97) 10−15 | ... |
J1512.7 − 0905 | (2.23 ± 0.11) 10−9 | (1.54 ± 0.08) 10−10 | (8.83 ± 0.80) 10−12 | (2.81 ± 0.79) 10−13 | (5.02 ± 5.63) 10−15 | ... | ... |
J1522.2+3143 | (9.36 ± 0.73) 10−10 | (7.16 ± 0.40) 10−11 | (4.87 ± 0.56) 10−12 | (1.54 ± 0.54) 10−13 | (4.95 ± 4.99) 10−15 | (1.59 ± 1.59) 10−15 | ... |
J1543.1+6130 | (9.39 ± 5.10) 10−11 | (9.49 ± 2.63) 10−12 | (1.06 ± 0.27) 10−12 | (1.23 ± 0.49) 10−13 | ... | ... | ... |
J1653.9+3946 | (7.02 ± 6.26) 10−11 | (1.52 ± 0.31) 10−11 | (1.97 ± 0.38) 10−12 | (2.27 ± 0.65) 10−13 | (3.90 ± 1.45) 10−14 | (3.06 ± 2.17) 10−15 | (5.41 ± 5.40) 10−16 |
J1719.3+1746 | (1.46 ± 0.61) 10−10 | (2.47 ± 0.23) 10−11 | (4.31 ± 0.48) 10−12 | (3.68 ± 0.83) 10−13 | (3.61 ± 1.37) 10−14 | (2.94 ± 2.04) 10−15 | ... |
J1751.5+0935 | (6.53 ± 0.86) 10−10 | (4.74 ± 3.22) 10−11 | (3.92 ± 5.53) 10−12 | (2.64 ± 0.69) 10−13 | (1.27 ± 0.82) 10−14 | ... | ... |
J1849.4+6706 | (5.03 ± 0.71) 10−10 | (4.55 ± 0.32) 10−11 | (4.60 ± 0.50) 10−12 | (2.57 ± 0.65) 10−13 | (9.51 ± 6.80) 10−15 | ... | ... |
J2000.2+6506 | ... | (2.13 ± 0.40) 10−11 | (1.88 ± 0.39) 10−12 | (9.78 ± 4.44) 10−14 | (5.06 ± 1.61) 10−14 | (1.58 ± 1.58) 10−15 | ... |
J2143.2+1741 | (3.96 ± 0.29) 10−10 | (2.77 ± 0.25) 10−11 | (2.12 ± 0.34) 10−12 | ... | ... | ... | ... |
J2158.8 − 3014 | (6.14 ± 0.67) 10−10 | (7.50 ± 0.55) 10−11 | (8.66 ± 0.79) 10−12 | (9.41 ± 1.38) 10−13 | (9.60 ± 2.38) 10−14 | ... | ... |
J2202.4+4217 | (2.30 ± 0.76) 10−10 | (2.57 ± 0.45) 10−11 | (2.27 ± 0.45) 10−12 | (7.49 ± 4.05) 10−14 | ... | ... | ... |
J2254.0+1609 | (9.76 ± 0.17) 10−9 | (6.73 ± 0.12) 10−10 | (4.59 ± 0.17) 10−11 | (1.54 ± 0.17) 10−12 | (1.97 ± 1.00) 10−14 | ... | ... |
J2327.3+0947 | (5.98 ± 0.71) 10−10 | (3.62 ± 0.43) 10−11 | (1.69 ± 0.37) 10−12 | ... | ... | ... | ... |
J2345.5 − 1559 | (4.25 ± 0.59) 10−10 | (2.76 ± 0.26) 10−11 | (1.56 ± 0.38) 10−12 | (9.21 ± 4.44) 10−14 | ... | ... | ... |
As a cross check a deconvolution technique (unfolding; Mazziotta 2009) has been used to reconstruct the source energy spectra from the observed data, after background subtraction. This method allows us to reconstruct the source spectrum from the data without assuming any spectral model, also taking into account the finite energy dispersion of the detector. The results of the two different methods are consistent as illustrated in Appendix A.
Once the differential flux in each energy bin ϕ(E) has been evaluated, the corresponding SED is then obtained by multiplying the differential flux by the square of the central energy value of that bin, i.e., νF(ν) = E2ϕ(E) where E = hν. The vertical error bars represent only the statistical errors. The systematic uncertainties in the effective area for the Pass6 V3 DIFFUSE event selection have been estimated to be 10% at 100 MeV, 5% at 562 MeV, and 20% for energies greater than 10 GeV (Abdo et al. 2009c).
3.2. Swift Data
The Swift Gamma-Ray-Burst (GRB) Explorer (Gehrels et al. 2004) is a multi-frequency, rapid response space observatory that was launched on 2004 November 20. To fulfill its purposes Swift carries three instruments on board: the Burst Alert Telescope (BAT; Barthelmy et al. 2005) sensitive in the 15–150 keV band, the X-Ray Telescope (XRT; Burrows et al. 2005) sensitive in the 0.3–10.0 keV band, and the UV and Optical Telescope (170–600 nm, UVOT; Roming et al. 2005). The very wide spectral range covered by these three instruments is of crucial importance for blazar issues as it covers where the transition between the synchrotron and inverse Compton emission usually occurs.
The primary objective of the Swift scientific program is the discovery and rapid follow-up of GRBs. However, as these elusive sources explode at random times and their frequency of occurrence is subject to large statistical fluctuations, there are periods when Swift is not engaged with GRB observations and the observatory can be used for different scientific purposes. The sources observed through this secondary science program are usually called Swift fill-in targets. Since the beginning of its activities Swift has observed hundreds of blazars as part of the fill-in program (e.g., Giommi et al. 2007). With the launch of AGILE and Fermi, the rate of Swift blazar observations increased significantly, leading to the observation (and detection) of all but six blazars in the LBAS sample.
The Swift database currently includes 119 observations of 48 LBAS blazars that were carried out either simultaneously or within three months of the Fermi LBAS data taking period. We used the UVOT, XRT, and BAT data of these observations to build our SED. Some blazars were observed several times in the period that we consider in this paper; in such cases, we considered only the exposures where the source was detected at minimum and maximum intensity by the XRT instrument.
3.2.1. UVOT Data Analysis
Swift observations are normally carried out so that UVOT produces a series of images in each of the lenticular filters (V, B, U, UVW1, UVM2, and UVW2). The photometry analysis of all our sources was performed using the standard UVOT software distributed within the HEAsoft 6.3.2 package and the calibration included in the latest release of the "Calibration Database." Counts were extracted from an aperture of 5'' radius for all filters and converted to fluxes using the standard zero points (Poole et al. 2008). The fluxes were then de-reddened using the appropriate values of E(B − V) for each source taken from Schlegel et al. (1998) with Aλ/E(B − V) ratios calculated for UVOT filters using the mean interstellar extinction curve from Fitzpatrick (1999). No variability was detected within single exposures in any filter.
The results of our analysis are summarized in Table 3 where Column 1 gives the source name, Column 2 gives the observation date, and the other columns report the magnitudes in the five UVOT filters with the own errors.
Table 3. Results of Swift UVOT Analysis
Source Name | Observation Date | Vmaga | Bmaga | Umaga | UVW1a | UVM2a | UVW2a |
---|---|---|---|---|---|---|---|
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) |
J0033.5 − 1921 | 2008 Nov 11 | 16.30 ± 0.04 | 16.59 ± 0.03 | 15.67 ± 0.03 | 15.59 ± 0.04 | 15.44 ± 0.04 | 15.60 ± 0.03 |
... | 2008 Nov 15 | 16.33 ± 0.07 | 16.60 ± 0.05 | 15.65 ± 0.04 | 15.59 ± 0.05 | 15.44 ± 0.05 | 15.57 ± 0.04 |
J0050.5 − 0928 | 2008 Jun 4 | ... | ... | ... | ... | ... | 15.074 ± 0.033 |
J0137.1+4751 | 2008 Nov 18 | 15.43 ± 0.03 | 15.84 ± 0.02 | 15.14 ± 0.04 | 15.38 ± 0.05 | 15.18 ± 0.04 | 15.43 ± 0.04 |
... | 2008 Feb 11 | ... | ... | ... | ... | ... | ... |
... | 2007 Nov 22 | 15.007 ± 0.02 | 15.554 ± 0.019 | 14.966 ± 0.023 | 13.354 ± 0.033 | 15.632 ± 0.036 | 15.772 ± 0.033 |
J0210.7 − 5100 | 2005 May 4 | ... | ... | ... | ... | ... | ... |
... | 2008 Dec 26 | 17.553 ± 0.062 | 17.037 ± 0.039 | 18.059 ± 0.046 | 16.784 ± 0.043 | 16.679 ± 0.044 | 17.058 ± 0.039 |
... | 2008 Oct 23 | 16.849 ± 0.046 | 16.490 ± 0.034 | 17.419 ± 0.036 | 16.511 ± 0.042 | 16.378 ± 0.043 | 16.726 ± 0.036 |
... | 2008 Aug 31 | 17.465 ± 0.102 | 18.035 ± 0.076 | 16.993 ± 0.06 | 16.875 ± 0.062 | 16.756 ± 0.068 | 17.073 ± 0.054 |
J0222.6+4302 | 2008 Oct 3 | 14.07 ± 0.03 | 14.37 ± 0.02 | 13.46 ± 0.02 | 13.43 ± 0.03 | 13.25 ± 0.04 | 13.40 ± 0.03 |
... | 2008 Oct 5 | 14.312 ± 0.019 | 14.640 ± 0.018 | 13.790 ± 0.022 | 13.88 ± 0.032 | 13.901 ± 0.032 | 13.989 ± 0.031 |
... | 2005 Nov 27 | 15.054 ± 0.014 | 15.528 ± 0.016 | 14.757 ± 0.02 | 14.939 ± 0.03 | 15.03 ± 0.03 | 15.149 ± 0.03 |
... | 2005 Jun 29 | 14.798 ± 0.018 | 15.298 ± 0.018 | 14.476 ± 0.021 | 14.638 ± 0.031 | 14.723 ± 0.032 | 14.840 ± 0.031 |
J0229.3 − 3640 | 2008 Nov 7 | 18.41 ± 0.20 | 19.12 ± 0.17 | 18.19 ± 0.12 | 18.47 ± 0.13 | 18.58 ± 0.16 | 19.38 ± 0.17 |
J0238.4+2855 | 2007 Jul 16 | ... | ... | ... | 17.928 ± 0.046 | ... | ... |
... | 2007 Jul 6 | ... | ... | ... | ... | ... | 18.671 ± 0.042 |
... | 2008 Sep 6 | ... | ... | ... | 17.21 ± 0.05 | ... | ... |
J0238.6+1636 | 2007 Feb 19 | ... | ... | 16.336 ± 0.041 | 16.514 ± 0.048 | 16.679 ± 0.053 | 17.024 ± 0.047 |
... | 2005 Jul 7 | 19.284 ± 0.258 | 19.876 ± 0.22 | 19.712 ± 0.225 | 19.326 ± 0.11 | 19.816 ± 0.120 | 19.863 ± 0.093 |
... | 2008 Oct 22 | 16.089 ± 0.057 | 16.964 ± 0.051 | 17.021 ± 0.072 | 17.198 ± 0.079 | 17.306 ± 0.094 | 17.552 ± 0.070 |
... | 2008 Sep 2 | 16.75 ± 0.10 | 17.69 ± 0.10 | 17.90 ± 0.15 | 17.88 ± 0.14 | 18.32 ± 0.21 | 18.31 ± 0.13 |
J0349.8 − 2102 | 2008 Oct 15 | 18.17(UL) | 19.22(UL) | 18.73(UL) | 18.88(UL) | 18.40(UL) | 19.14(UL) |
J0423.1 − 0112 | 2007 Mar 24 | 17.501 ± 0.061 | 18.024 ± 0.045 | 17.327 ± 0.041 | 17.456 ± 0.048 | 17.659 ± 0.053 | 17.908 ± 0.045 |
... | 2008 Jan 3 | ... | 17.185 ± 0.022 | ... | ... | ... | ... |
... | 2008 Aug 6 | 17.237 ± 0.129 | 17.955 ± 0.099 | 17.151 ± 0.081 | 17.218 ± 0.08 | 17.249 ± 0.085 | 17.607 ± 0.074 |
J0428.7-3755 | 2008 Oct 27 | ... | ... | ... | ... | 19.97 ± 0.97 | ... |
J0449.7 − 4348 | 2008 Dec 19 | 14.33 ± 0.02 | 14.57 ± 0.02 | 13.62 ± 0.02 | 13.49 ± 0.03 | 13.32 ± 0.03 | 13.39 ± 0.03 |
... | 2009 Jan 12 | 14.251 ± 0.014 | 14.534 ± 0.016 | 13.591 ± 0.02 | 13.476 ± 0.03 | 13.324 ± 0.03 | 13.425 ± 0.03 |
J0457.1-2325 | 2008 Nov 16 | ||||||
... | 2008 Oct 26 | 17.011 ± 0.055 | 17.507 ± 0.035 | 16.770 ± 0.035 | 16.907 ± 0.044 | 16.983 ± 0.058 | 17.457 ± 0.044 |
J0507.9+6739 | 2009 Jan 4 | 16.15 ± 0.04 | 16.43 ± 0.04 | 15.47 ± 0.04 | 15.35 ± 0.04 | 15.19 ± 0.04 | 15.29 ± 0.04 |
J0516.2 − 6200 | 2009 Jan 11 | 17.441 ± 0.035 | 17.881 ± 0.026 | 17.171 ± 0.028 | 17.359 ± 0.037 | 17.413 ± 0.041 | 17.778 ± 0.037 |
... | 2009 Jan 15 | 17.668 ± 0.068 | 18.053 ± 0.046 | 17.262 ± 0.043 | 17.546 ± 0.054 | 17.586 ± 0.060 | 18.058 ± 0.052 |
J0531.0+1331 | 2006 Apr 12 | 18.20 (UL) | 19.03 (UL) | 18.57(UL) | 18.63(UL) | ... | ... |
2006 Mar 28 | 18.57(UL) | 19.08(UL) | 18.90(UL) | 18.94(UL) | ... | ... | |
2008 Sep 23 | 17.99(UL) | 18.71(UL) | 18.22(UL) | 18.16(UL) | 17.63(UL) | 18.21 (UL) | |
2008 Oct 22 | ... | ... | ... | 19.51(UL) | ... | ... | |
J0538.8 − 4403 | 2005 Jan 26 | ... | ... | ... | ... | ... | ... |
... | 2005 Nov 17 | 16.443 ± 0.018 | 16.152 ± 0.022 | 16.912 ± 0.019 | ... | ... | ... |
... | 2008 Oct 12 | ... | 16.585 ± 0.033 | 15.904 ± 0.034 | 16.039 ± 0.042 | ... | 16.292 ± 0.040 |
... | 2008 Oct 7 | 15.867 ± 0.027 | 16.315 ± 0.022 | 15.967 ± 0.027 | 15.730 ± 0.034 | 15.757 ± 0.036 | 15.967 ± 0.033 |
J0712.9+5034 | 2009 Jan 21 | 16.070 ± 0.043 | 17.516 ± 0.032 | 16.794 ± 0.033 | 16.983 ± 0.041 | 17.100 ± 0.045 | 17.176 ± 0.038 |
J0722.0+7120 | 2005 Apr 4 | 14.024 ± 0.013 | 14.490 ± 0.016 | 13.553 ± 0.020 | 12.522 ± 0.03 | 13.479 ± 0.03 | 12.618 ± 0.03 |
... | 2008 Dec 13 | 13.403 ± 0.017 | 13.793 ± 0.017 | 13.048 ± 0.021 | 13.126 ± 0.031 | 13.104 ± 0.032 | 13.216 ± 0.031 |
... | 2008 Apr 28 | 12.853 ± 0.014 | 13.233 ± 0.016 | 12.340 ± 0.020 | 12.334 ± 0.030 | 12.277 ± 0.030 | 12.384 ± 0.030 |
... | 2007 Nov 3 | 13.114 ± 0.014 | 13.500 ± 0.016 | 12.650 ± 0.020 | 12.685 ± 0.03 | 12.777 ± 0.03 | 12.660 ± 0.031 |
J0730.4 − 1142 | 2007 Dec 8 | ... | ... | ... | ... | 18.77(UL) | ... |
... | 2007 Sep 27 | ... | ... | ... | ... | ... | ... |
... | 2008 Dec 6 | ... | ... | ... | ... | 17.62 ± 0.29 | ... |
... | 2008 Nov 8 | ... | 16.70-13.85 | 17.99 − 17.96 | |||
J0855.4+2009 | 2007 Nov 7 | ... | ... | ... | 13.91 ± 0.03 | ... | ... |
2005 May 20 | 15.00 ± 0.02 | 14.65 ± 0.06 | |||||
2008 Oct 30 | 14.821 ± 0.041 | 15.299 ± 0.024 | 14.677 ± 0.024 | 14.863 ± 0.033 | ... | ... | |
2008 Nov 8 | 14.82 ± 0.03 | 15.31 ± 0.02 | 14.65 ± 0.03 | 14.82 ± 0.04 | ... | 15.00 ± 0.04 | |
J0921.2+4437 | 2009 Jan 18 | 17.307 ± 0.048 | 17.692 ± 0.034 | 17.033 ± 0.035 | 18.365 ± 0.065 | 20.948 ± 0.312 | 19.976 ± 0.110 |
J1015.2+4927 | 2007 Sep 24 | ... | ... | ... | ... | ... | ... |
2005 Jun 26 | ... | ... | ... | ... | ... | ... | |
2008 May 2 | 15.312 ± 0.042 | 15.574 ± 0.029 | 14.631 ± 0.030 | 14.402 ± 0.037 | 14.233 ± 0.040 | 14.312 ± 0.034 | |
2008 May 8 | 15.288 ± 0.03 | 15.533 ± 0.023 | 14.589 ± 0.025 | 14.423 ± 0.033 | 14.233 ± 0.035 | 14.310 ± 0.032 | |
J1057.8+0138 | 2007 Apr 9 | ... | ... | ... | ... | ... | ... |
2008 Jul 19 | ... | ... | ... | ... | 16.980 ± 0.048 | ... | |
J1058.9+5629 | 2009 Jan 21 | 15.424 ± 0.016 | ... | 14.884 ± 0.021 | ... | ... | 14.767 ± 0.031 |
J1104.5+3811 | 2005 Mar 1 | ... | ... | ... | ... | ... | ... |
2006 Jun 24 | ... | ... | ... | ... | ... | ... | |
2008 Jun 12 | ... | ... | ... | 11.91 ± 0.03 | 11.64 ± 0.03 | 11.75 ± 0.03 | |
2008 Dec 5 | ... | ... | ... | 12.54 ± 0.03 | 12.25 ± 0.03 | 12.35 ± 0.03 | |
J1159.2+2912 | 2007 Nov 24 | ... | ... | 17.277 ± 0.022 | ... | ... | ... |
2007 Jun 27 | ... | ... | ... | ... | 16.24 ± 0.04 | ... | |
2008 Nov 21 | ... | ... | ... | 16.849 ± 0.032 | ... | ... | |
J1221.7+2814 | 2008 Jun 7 | 14.677 ± 0.017 | 15.050 ± 0.017 | 14.214 ± 0.021 | 14.169 ± 0.030 | 14.011 ± 0.021 | 14.169 ± 0.030 |
... | 2008 Dec 28 | 15.081 ± 0.030 | 15.481 ± 0.022 | 14.961 ± 0.025 | 14.703 ± 0.034 | 14.902 ± 0.085 | 14.876 ± 0.033 |
... | 2008 Mar 28 | 14.649 ± 0.024 | 15.031 ± 0.020 | 14.200± 0.023 | 14.155 ±0.033 | 14.072 ± 0.033 | 14.201 ± 0.032 |
... | 2005 Jul 14 | 15.283 ± 0.033 | 15.681 ± 0.032 | 14.870 ± 0.029 | 14.957 ± 0.038 | 14.874 ± 0.039 | 14.957 ± 0.033 |
J1229.1+0202 | 2005 Nov 24 | ... | ... | ... | ... | ... | ... |
2006 May 26 | ... | ... | ... | ... | ... | ... | |
2008 May 10 | 12.67 ± 0.02 | ... | 11.82 ± 0.02 | 11.34 ± 0.03 | 11.14 ± 0.03 | ... | |
2008 Jun 1 | 12.65 ± 0.02 | 12.89 ± 0.02 | 11.82 ± 0.02 | 11.38 ± 0.03 | 11.15 ± 0.03 | 11.15 ± 0.03 | |
J1248.7+5811 | 2008 May 15 | 15.6477 ± 0.032 | 16.0047 ± 0.025 | 15.1167 ± 0.027 | 15.0747 ± 0.035 | 14.9637 ± 0.036 | 15.1067 ± 0.033 |
J1256.1 − 0547 | 2007 Jan 13 | 13.421 ± 0.014 | 13.927 ± 0.016 | 13.196 ± 0.02 | 13.349 ± 0.030 | 13.397 ± 0.031 | 13.559 ± 0.030 |
... | 2007 Jul 12 | 14.671 ± 0.018 | 15.173 ± 0.018 | 14.428 ± 0.022 | 14.601 ± 0.032 | 14.608 ± 0.032 | 14.795 ± 0.031 |
... | 2008 Aug 20 | 16.381 ± 0.065 | 16.680 ± 0.04 | 15.868 ± 0.036 | 15.886 ± 0.042 | 15.835 ± 0.066 | 15.956 ± 0.037 |
... | 2008 Aug 18 | 16.597 ± 0.084 | 17.104 ± 0.058 | 16.148 ± 0.044 | 16.244 ± 0.049 | 16.107 ± 0.052 | 16.252 ± 0.041 |
J1310.6+3220 | 2007 Aug 1 | 16.781 ± 0.044 | 17.277 ± 0.033 | 16.491 ± 0.033 | 16.623 ± 0.037 | 16.667 ± 0.045 | 16.937 ± 0.038 |
... | 2007 Apr 2 | 17.417 ± 0.048 | 16.949 ± 0.064 | 16.594 ± 0.044 | 16.649 ± 0.050 | 16.661 ± 0.057 | 16.949 ± 0.046 |
... | 2008 May 12 | ... | ... | ... | ... | 17.335 ± 0.036 | ... |
... | 2008 Aug 20 | ... | ... | ... | ... | 16.715 ± 0.034 | ... |
J1457.6 − 3538 | 2008 Jan 1 | ... | ... | ... | ... | 18.432 ± 0.042 | ... |
... | 2008 Sep 7 | 16.807 ± 0.093 | 17.588 ± 0.061 | 16.789 ± 0.053 | 17.159 ± 0.065 | 17.584 ± 0.152 | 18.138 ± 0.079 |
J1504.4+1030 | 2007 Jan 1 | 18.14 ± 0.10 | 18.61 ± 0.07 | 17.70 ± 0.05 | 18.20 ± 0.06 | ... | ... |
2007 Feb 2 | 18.66 ± 0.00 | 19.53 ± 0.34 | 18.25 ± 0.17 | 18.53 ± 0.18 | ... | ... | |
2008 Aug 8 | 16.54 ± 0.03 | 16.95 ± 0.02 | 16.21 ± 0.03 | 16.42 ± 0.04 | 16.43 ± 0.04 | 16.63 ± 0.03 | |
2008 Aug 20 | ... | ... | ... | ... | ... | ... | |
J1512.7 − 0905 | 2009 Jan 16 | ... | ... | 15.84 ± 0.04 | 15.90 ± 0.05 | 15.65 ± 0.04 | 15.76 ± 0.05 |
J1522.2+3143 | 2008 Nov 12 | 19.776 ± 0.403 | 20.173 ± 0.272 | 18.975 ± 0.142 | 19.499 ± 0.153 | 20.061 ± 0.042 | 21.174 ± 0.305 |
J1543.1+6130 | 2009 Jan 18 | 16.465 ± 0.043 | 16.741 ± 0.029 | 15.929 ± 0.030 | 15.963 ± 0.038 | 15.901 ± 0.039 | 16.023 ± 0.035 |
... | 2009 Jan 20 | 16.332 ± 0.031 | 16.723 ± 0.024 | 15.804 ± 0.025 | 15.810 ± 0.034 | 15.769 ± 0.035 | 15.879 ± 0.032 |
J1653.9+3946 | 2008 May 12 | ... | ... | ... | ... | ... | ... |
J1719.3+1746 | 2009 Jan 8 | 17.764 ± 0.099 | 18.101 ± 0.055 | 17.291 ± 0.046 | 17.390 ± 0.048 | 17.378 ± 0.056 | 17.610 ± 0.046 |
J1751.5+0935 | 2008 Jan 24 | ... | ... | ... | 16.40 ± 0.06 | ... | ... |
J1849.4+6706 | 2006 Jun 11 | 17.715 ± 0.059 | 18.150 ± 0.045 | 17.483 ± 0.043 | 17.544 ± 0.045 | ... | ... |
... | 2007 Jan 23 | 17.492 ± 0.139 | 17.830 ± 0.082 | 17.120 ± 0.075 | 17.230 ± 0.080 | ... | ... |
... | 2008 Aug 4 | ... | ... | ... | 16.141 ± 0.035 | ... | ... |
J2000.2+6506 | 2006 May 23 | 14.982 ± 0.019 | 15.493 ± 0.045 | 14.720 ± 0.022 | 14.921 ± 0.032 | 15.031 ± 0.033 | 15.011 ± 0.034 |
... | 2006 Jun 22 | ... | ... | ... | ... | ... | 15.389 ± 0.037 |
... | 2008 Oct 13 | 15.085 ± 0.033 | 15.564 ± 0.026 | 14.728 ± 0.028 | 14.969 ± 0.038 | 15.050 ± 0.044 | 15.060 ± 0.035 |
... | 2008 Oct 31 | 15.076 ± 0.034 | 15.587 ± 0.027 | 14.952 ± 0.030 | 15.211 ± 0.041 | 15.346 ± 0.047 | 15.450 ± 0.038 |
J2143.2+1741 | 2007 Apr 23 | ... | ... | ... | ... | 15.169 ± 0.033 | 15.130 ± 0.030 |
2008 Jan 1 | ... | ... | ... | ... | ... | ... | |
... | 2009 Jan 15 | ... | ... | ... | ... | 15.007 ± 0.031 | ... |
J2158.8 − 3014 | 2006 Aug 1 | ... | ... | ... | ... | ... | ... |
... | 2006 Apr 30 | 13.023 ± 0.013 | 13.349 ± 0.016 | 12.445 ± 0.020 | 12.341 ± 0.03 | 12.259 ± 0.030 | 12.387 ± 0.03 |
... | 2008 Sep 5 | 13.077 ± 0.017 | 13.364 ± 0.017 | 12.367 ± 0.020 | 12.206 ± 0.03 | 12.09 ± 0.031 | 12.178 ± 0.03 |
... | 2008 Oct 17 | 13.441 ± 0.018 | 13.747 ± 0.017 | 12.787 ± 0.021 | 12.691 ± 0.031 | 12.566 ± 0.031 | 12.667 ± 0.03 |
J2202.4+4217 | 2008 Sep 4 | 13.80 ± 0.04 | 14.33 ± 0.04 | 13.60 ± 0.04 | 13.74 ± 0.04 | 13.78 ± 0.05 | 13.96 ± 0.04 |
J2254.0+1609 | |||||||
J2327.7+0947 | 2008 Jun 3 | ... | ... | 17.748 ± 0.028 | ... | ... | ... |
J2345.5 − 1559 | 2009 Jan 10 | 18.494 ± 0.128 | 18.598 ± 0.062 | 17.923 ± 0.053 | 17.786 ± 0.047 | 17.664 ± 0.052 | 17.780 ± 0.039 |
3.2.2. XRT Data Analysis
The XRT is usually operated in the auto state mode which automatically adjusts the readout mode of the CCD detector to the source brightness, in an attempt to avoid pile-up (see Burrows et al. 2005; Hill et al. 2004, for details of the XRT observing modes). Given the low count rate of our blazars most of the data were collected using the most sensitive photon counting (PC) mode while the windowed timing (WT) mode was used for bright sources with shorter exposures.
The XRT data were processed with the XRTDAS software package (ver. 2.4.1) developed at the ASDC and distributed by the NASA High Energy Astrophysics Archive Research Center (HEASARC) within the HEASoft package (ver. 6.6.1). Event files were calibrated and cleaned with standard filtering criteria with the xrtpipeline task using the latest calibration files available in the Swift CALDB. Events in the energy range 0.3–10 keV with grades 0–12 (PC mode) and 0–2 (WT mode) were used for the analysis.
Events for the spectral analysis were selected within a circle of 20 pixel (∼47'') radius, which encloses about 90% of the PSF at 1.5 keV (Moretti et al. 2005), centered on the source position. For PC mode data, when the source count rate is above ∼0.5 counts s−1 data are significantly affected by pile-up in the inner part of the point spread function (PSF). For such cases, after comparing the observed PSF profile with the analytical model derived by Moretti et al. (2005), we removed pile-up effects by excluding events detected within up to 6 pixels from the source position, and used an outer radius of 30 pixels. The value of the inner radius was evaluated individually for each observation affected by pile-up, depending on the observed count rate.
Ancillary response files were generated with the xrtmkarf task applying corrections for the PSF losses and CCD defects. Source spectra were binned to ensure a minimum of 20 counts per bin to utilize the χ2 minimization fitting technique.
We fitted the spectra adopting an absorbed power-law model with photon index Γx. When deviations from a single power-law model were found, we adopted a log-parabolic law of the form F(E) = KE(−a+b·log(E)) (Massaro et al. 2004) which has been shown to fit well the X-ray spectrum of blazars (e.g., Giommi et al. 2005; Tramacere et al. 2009). This spectral model is described by only two parameters: a, the photon index at 1 keV, and b, the curvature of the parabola. For both models the amount of hydrogen-equivalent column density (NH) was fixed to the Galactic value along the line of sight (Kalberla et al. 2005).
The results of the spectral fits are shown in Table 4 where Column 1 gives the source name, Column 2 gives the observation date, Column 3 gives the net XRT exposure time, Column 4 gives the 2–10 keV X-ray flux, Column 5 gives the best-fit photon index Γx or the log parabola parameter a when a simple power-law model was not a good representation of the data, Column 6 gives the best-fit curvature parameter b, Column 7 gives the number of degrees of freedom, and Column 8 gives the value of the reduced χ2.
Table 4. Results of Swift XRT Data Analysis
Source Name | Observation Date | XRT Exposure (s) | X-ray Flux (2–10 keV)a | Γx/ab | b | dof | χ2reduced |
---|---|---|---|---|---|---|---|
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) |
J0033.5 − 1921 | 2008 Nov 11 | 2946.2 | 2.32 × 10−12 | 2.29 ± 0.07 | −0.15 ± 0.27 | 23 | 1.03 |
... | 2008 Nov 15 | 3939.8 | 1.86 × 10−12 | 2.4 ± 0.06 | −0.29 ± 0.24 | 31 | 1.3 |
J0050.5 − 0928 | 2008 Jun 4 | 865 | 1.27 × 10−12 | ... | ... | ... | ... |
J0137.1+4751 | 2008 Nov 18 | 6520 | 2.4 × 10−12 | 1.38 ± 0.11 | ... | 11 | 1.51 |
... | 2008 Feb 11 | 4674 | 1.7 × 10−12 | 1.59 ± 0.16 | ... | 4 | 1.6 |
... | 2007 Nov 22 | 4643 | 2.2 × 10−12 | 1.58 ± 0.01 | ... | 11 | 1.19 |
J0210.7 − 5100 | 2005 May 4 | 2102 | 1.89 × 10−12 | 1.85 ± 0.12 | ... | 6 | 0.53 |
... | 2008 Dec 26 | 4595 | 1.28 × 10−12 | 1.66 ± 0.13 | ... | 7 | 1.93 |
... | 2008 Oct 23 | 3688 | 2.67 × 10−12 | 1.64 ± 0.08 | ... | 14 | 1.13 |
... | 2008 Aug 31 | 1475 | 1.39 × 10−12 | ... | ... | ... | ... |
J0222.6+4302 | 2008 Oct 3 | 4525 | 4.16 × 10−12 | 2.67 ± 0.39 | ... | 72 | 0.90 |
... | 2008 Oct 5 | 2704 | 2.09 × 10−12 | 2.80 ± 0.70 | ... | 29 | 0.87 |
... | 2005 Nov 27 | 52415 | 2.15 × 10−12 | 2.3 ± 0.02 | ... | 215 | 1.022 |
... | 2005 Jun 29 | 5541 | 1.74 × 10−12 | 2.34 ± 0.07 | ... | 25 | 1.44 |
J0229.3 − 3640 | 2008 Nov 7 | 12428 | 9.64 × 10−13 | 1.03 ± 0.15 | −0.52 ± 0.27 | 12 | 0.54 |
J0238.4+2855 | 2007 Jul 16 | 7269 | 1.6 × 10−12 | 1.56 ± 0.10 | ... | 10 | 0.64 |
... | 2007 Jun 6 | 2901 | 1.57 × 10−12 | 1.55 ± 0.14 | ... | 4 | 1.06 |
... | 2008 Sep 6 | 2417 | 1.44 × 10−12 | ... | ... | ... | ... |
J0238.6+1636 | 2007 Feb 19 | 1936 | 1.026 × 10−11 | 1.14 ± 0.08 | ... | 15 | 0.58 |
... | 2005 Jul 7 | 12042 | 1.64 × 10−12 | 1.44 ± 0.07 | ... | 20 | 1.46 |
... | 2008 Oct 22 | 1198 | 2.24 × 10−11 | 1.93 ± 0.06 | ... | 26 | 1.74 |
... | 2008 Sep 2 | 6944 | 3.8 × 10−12 | 1.37 ± 0.06 | ... | 26 | 1.7 |
J0349.8 − 2102 | 2008 Oct 15 | 1557 | 7.8 × 10−13 | ... | ... | ... | ... |
J0423.1 − 0112 | 2007 Mar 23 | 7044 | 2.54 × 10−12 | 1.71 ± 0.06 | ... | 25 | 0.93 |
... | 2008 Jan 3 | 5536 | 2.39 × 10−12 | 1.57 ± 0.08 | ... | 14 | 0.45 |
... | 2008 Aug 6 | 1306 | 4.65 × 10−12 | 1.56 ± 0.13 | ... | 5 | 0.75 |
J0428.7 − 3755 | 2008 Oct 27 | 4483 | 7.07 × 10−13 | 1.89 ± 0.14 | ... | 5 | 0.96 |
J0449.7 − 4348 | 2008 Dec 19 | 7981 | 7.6 × 10−12 | 2.53 ± 0.02 | −0.36 ± 0.06 | 165 | 1.07 |
... | 2009 Jan 12 | 10967 | 2.53 × 10−12 | 2.85 ± 0.03 | −0.38 ± 0.09 | 122 | 1.14 |
J0457.1 − 2325 | 2008 Nov 16 | 3034 | 6.33 × 10−13 | ... | ... | ... | ... |
... | 2008 Oct 25 | 3970.1 | 7.92 × 10−13 | 1.9 ± 0.3 | ... | 4 | 0.01 |
J0507.9+6739 | 2009 Jan 4 | 28998 | 4.41 × 10−11 | 2.29 ± 0.03 | ... | 388 | 1.06 |
J0516.2 − 6200 | 2009 Jan 11 | 14024 | 7.49 × 10−13 | 1.70 ± 0.09 | ... | 11 | 1.06 |
... | 2009 Jan 15 | 4343 | 5.18 × 10−13- | ... | ... | ... | |
J0531.0+1331 | 2006 Apr 12 | 2572 | 5.3 × 10−12 | 1.4 ± 0.1 | ... | 11 | 1.84 |
... | 2006 Mar 28 | 3332 | 3.3 × 10−12 | 1.33 ± 0.15 | ... | 7 | 0.67 |
... | 2008 Sep 23 | 1982 | 4.42 × 10−12 | 1.14 ± 0.17 | ... | 4 | 0.59 |
... | 2008 Oct 22 | 2471 | 2.9 × 10−12 | ... | ... | ... | ... |
J0538.8 − 4403 | 2005 Jan 26 | 7438 | 8.30 × 10−12 | 1.78 ± 0.03 | ... | 97 | 1.04 |
2005 Nov 17 | 6431 | 2.15 × 10−12 | 1.84 ± 0.06 | ... | 22 | 1.00 | |
2008 Oct 12 | 1413 | 4.72 × 10−12 | 1.69 ± 0.09 | ... | 9 | 0.31 | |
2008 Oct 7 | 5054 | 4.33 × 10−12 | 1.70 ± 0.05 | ... | 32 | 0.98 | |
J0712.9+5034 | 2009 Jan 21 | 6234 | 3.67 × 10−13 | ... | ... | ... | ... |
J0722.0+7120 | 2005 Apr 4 | 18887 | 1.06 × 10−12 | 2.78 ± 0.05 | ... | 48 | 0.95 |
2008 Dec 13 | 1442 | 2.8 × 10−12 | 2.45 ± 0.13 | ... | 8 | 0.96 | |
2008 Apr 28 | 2002 | 9.7 × 10−12 | 2.7 ± 0.06 | ... | 44 | 1.25 | |
2007 Nov 3 | 2802 | 6.82 × 10−12 | 2.6 ± 0.05 | ... | 38 | 0.85 | |
J0730.4 − 1142 | 2007 Dec 8 | 6028 | 1.45 × 10−12 | 1.55 ± 0.14 | ... | 6 | 0.45 |
2007 Sep 27 | 1918 | 1.07 × 10−12 | ... | ... | ... | ... | |
2008 Dec 6 | 6234 | 1.47 × 10−12 | 1.72 ± 0.13 | ... | 8 | 1.29 | |
2008 Nov 8 | 1989 | 1.35 × 10−12 | ... | ... | ... | ... | |
J0855.4+2009 | 2007 Nov 7 | 1854 | 5.29 × 10−12 | 1.35 ± 0.12 | ... | 8 | 0.75 |
2005 May 20 | 3793 | 2.12 × 10−12 | 1.62 ± 0.09 | ... | 10 | 0.96 | |
2008 Oct 30 | 952 | 8.75 × 10−12 | 1.47 ± 0.12 | ... | 8 | 1.00 | |
2008 Nov 8 | 994 | 7.02 × 10−12 | 1.43 ± 0.12 | ... | 5 | 0.84 | |
J0921.2+4437 | 2009 Jan 18 | 6534 | 2.86 × 10−12 | 1.63 ± 0.06 | ... | 22 | 1.04 |
J1015.2+4927 | 2007 Sep 24 | 2870 | 7.02 × 10−12 | 2.47 ± 0.04 | −0.49 ± 0.13 | 73 | 0.81 |
2005 Jun 26 | 9962 | 9.67 × 10−12 | 2.26 ± 0.02 | −0.09 ± 0.06 | 152 | 0.95 | |
2008 May 2 | 862 | 2.31 × 10−11 | 2.14 ± 0.06 | −0.53 ± 0.20 | 32 | 0.94 | |
2008 May 8 | 1769 | 1.01 × 10−11 | 2.47 ± 0.04 | −0.28 ± 0.15 | 50 | 0.92 | |
J1057.8+0138 | 2007 Apr 9 | 662 | 2.52 × 10−12 | ... | ... | ... | ... |
2008 Jul 19 | 1064 | 1.76 × 10−12 | ... | ... | ... | ... | |
J1058.9+5629 | 2009 Jan 21 | 3817 | 1.36 × 10−12 | 2.48 ± 0.05 | −0.47 ± 0.20 | 40 | 0.79 |
J1104.5+3811 | 2006 Jun 24 | 12944 | 1.10 × 10−09 | 1.86 ± 0.02 | −0.092 ± 0.004 | 802 | 3.6 |
2005 Mar 1 | 7197 | 4.14 × 10−11 | 2.60 ± 0.007 | −0.099 ± 0.002 | 320 | 1.35 | |
2008 Jun 12 | 4980 | 2.62 × 10−09 | 1.74 ± 0.004 | −0.202 ± 0.009 | 652 | 2.31 | |
2008 Dec 5 | 5361 | 2.69 × 10−10 | 2.190 ± 0.005 | −0.349 ± 0.013 | 496 | 1.88 | |
J1159.2+2912 | 2007 Nov 24 | 8268 | 1.29 × 10−12 | 1.71 ± 0.08 | ... | 14 | 1.22 |
2007 Jun 27 | 2767 | 8.09 × 10−13 | 1.63 ± 0.25 | ... | ... | ... | |
2008 Nov 21 | 6968 | 1.86 × 10−12 | 1.50 ± 0.09 | ... | 11 | 1.09 | |
1221.7+2814 | 2008 Jun 7 | 9087 | 5.14 × 10−12 | 2.04 ± 0.03 | −0.19 ± 0.08 | 130 | 1.03 |
... | 2008 Dec 28 | 1548 | 7.4 × 10−12 | ... | ... | ... | ... |
... | 2008 Mar 28 | 1705 | 1.9 × 10−12 | 2.4 ± 0.08 | −0.47 ± 0.29 | 17 | 0.94 |
... | 2005 Jul 14 | 1191 | 7.7 × 10−13 | ... | ... | ... | ... |
J1229.1+0202 | 2005 Nov 24 | 4008 | 1.33 × 10−10 | 1.68 ± 0.02 | ... | 143 | 1.31 |
2006 May 26 | 2349 | 9.9 × 10−11 | 1.68 ± 0.03 | ... | 80 | 1.13 | |
2008 May 10 | 2249 | 1.02 × 10−10 | 1.57 ± 0.02 | ... | 115 | 1.14 | |
2008 Jun 1 | 1313 | 7.9 × 10−11 | 1.64 ± 0.03 | ... | 62 | 0.86 | |
J1248.7+5811 | 2008 May 15 | 2283 | 6.19 × 10−13 | 2.42 ± 0.13 | −0.18 ± 0.49 | 5 | 1.18 |
J1256.1 − 0547 | 2008 Aug 18 | 1777 | 4.51 × 10−12 | 1.8 ± 0.09 | ... | 12 | 0.75 |
... | 2008 Aug 20 | 1922 | 6.05 × 10−12 | 1.8 ± 0.07 | ... | 22 | 1.34 |
... | 2007 Jul 12 | 4839 | 8.04 × 10−12 | 1.5 ± 0.04 | ... | 51 | 0.87 |
... | 2007 Jan 12 | 9700 | 1.27 × 10−11 | 1.6 ± 0.02 | ... | 150 | 1.36 |
J1310.6+3220 | 2007 Aug 1 | 4913 | 2.15 × 10−12 | 1.61 ± 0.09 | ... | 11 | 0.55 |
2007 Apr 2 | 2150 | 2.52 × 10−12 | 1.61 ± 0.11 | ... | 6 | 0.36 | |
2008 May 12 | 5342 | 1.62 × 10−12 | 1.66 ± 0.08 | ... | 12 | 1.13 | |
2008 Aug 20 | 4773 | 2.51 × 10−12 | 1.56 ± 0.08 | ... | 13 | 0.82 | |
J1457.6 − 3538 | 2008 Jan 1 | 9128 | 5.65 × 10−13 | 1.96 ± 0.13 | ... | 7 | 1.30 |
2008 Sep 7 | 1596 | 1.80 × 10−12 | ... | ... | ... | ... | |
J1504.4+1030 | 2007 Jan 1 | 10351 | 9.28 × 10−13 | 1.45 ± 0.1 | ... | 9 | 0.65 |
2007 Feb 2 | 5074 | 8.93 × 10−13 | ... | ... | ... | ... | |
2008 Aug 8 | 12466 | 1.66 × 10−12 | 1.53 ± 0.06 | ... | 27 | 1.22 | |
2008 Aug 20 | 1912 | 9.94 × 10−13 | ... | ... | ... | ... | |
J1512.7 − 0905 | 2009 Jan 16 | 7124 | 5.47 × 10−12 | 1.40 ± 0.10 | ... | 31 | 0.57 |
J1522.2+3143 | 2008 Nov 12 | 5884 | 2.68 × 10−13 | ... | ... | ... | ... |
J1543.1+6130 | 2009 Jan 18 | 3367 | 2.06 × 10−13 | ... | ... | ... | ... |
2009 Jan 20 | 6875 | 1.68 × 10−13 | ... | ... | ... | ... | |
J1653.9+3946 | 2008 May 12 | 1160 | 1.40 × 10−10 | 2.07 ± 0.07 | ... | 186 | 0.95 |
J1719.3+1746 | 2009 Jan 8 | 4808 | 9.28 × 10−13 | 1.70 ± 0.12 | ... | 5 | 1.42 |
J1751.5+0935 | 2009 Jan 24 | 983 | 2.71 × 10−12 | 1.97 ± 0.51 | ... | 8 | 0.8 |
J1849.4+6706 | 2006 Jun 11 | 8897 | 1.17 × 10−12 | 1.70 ± 0.09 | ... | 14 | 1.50 |
2007 Jan 23 | 1171 | 1.96 × 10−11 | ... | ... | ... | ... | |
2008 Aug 4 | 2206 | 2.48 × 10−12 | 1.47 ± 0.16 | ... | 4 | 0.63 | |
J2000.2+6506 | 2006 May 23 | 5372 | 2.14 × 10−10 | 1.91 ± 0.01 | −0.26 ± 0.02 | 488 | 1.31 |
2006 Jun 22 | 438 | 9.90 × 10−11 | 1.89 ± 0.09 | −0.44 ± 0.20 | 28 | 1.48 | |
2008 Oct 13 | 1204 | 1.22 × 10−10 | 1.82 ± 0.05 | −0.31 ± 0.11 | 72 | 1.15 | |
2008 Oct 31 | 1084 | 5.61 × 10−11 | 2.16 ± 0.05 | −0.25 ± 0.13 | 63 | 0.73 | |
J2143.2+1741 | 2007 Apr 23 | 7180 | 1.16 × 10−12 | 1.79 ± 0.10 | ... | 12 | 1.38 |
2009 Jan 15 | 5913 | 1.60 × 10−12 | 1.74 ± 0.10 | ... | 12 | 2.14 | |
J2158.8 − 3014 | 2006 Aug 1 | 1541 | 4.47 × 10−11 | 2.55 ± 0.03 | −0.37 ± 0.10 | 96 | 1.07 |
... | 2006 Apr 30 | 8217 | 1.5 × 10−11 | 2.52 ± 0.02 | −2.38 ± 0.06 | 149 | 1.00 |
... | 2008 Sep 5 | 1091 | 5.59 × 10−11 | 2.42 ± 0.01 | −0.10 ± 0.05 | 185 | 1.35 |
... | 2008 Oct 17 | 1229 | 1.83 × 10−11 | 2.35 ± 0.05 | −0.18 ± 0.14 | 41 | 1.03 |
J2202.4+4217 | 2008 Sep 4 | 5787 | 1.01 × 10−11 | 2.05 ± 0.15 | ... | 61 | 1.11 |
J2254.0+1609 | 2008 Aug 8 | 4216 | 3.32 × 10−11 | 1.55 ± 0.03 | ... | 91 | 1.30 |
J2327.7+0947 | 2008 Jun 3 | 4486 | 2.80 × 10−12 | 1.13 ± 0.09 | ... | 9 | 0.78 |
J2345.5 − 1559 | 2009 Jan 10 | 9503 | 2.41 × 10−13 | ... | ... | ... | ... |
Notes. aWhen the photon statistics were too poor to allow a reliable best fit, the flux was estimated converting the observed count rate assuming a power-law model with photon index of 1.9 and low energy absorption due to Galactic NH. bThis column gives the power-law photon index γ when a simple power-law model could be used. In the case where the log parabola model was used this column gives the a parameter which represents the photon index at 1 keV.
3.2.3. BAT Hard X-ray Data Analysis
We used survey data from the BAT on board Swift to produce 15–200 keV spectra of the blazars presented in this analysis. In order to do so, we used three years of survey data (see Ajello et al. 2009, for details) and extracted the spectra of those blazars that are significantly detected in the 15–55 keV band. Because of the very long integration time these data are not simultaneous with our Fermi data.
Only 15 blazars, among those presented here, were detected by BAT at a significance ⩾4 σ. The spectral extraction is performed as described in Ajello et al. (2008) and the background-subtracted spectra represent the average emissions of the sources within the time spanned by the BAT survey.
3.2.4. Swift Observations of LBAS Blazars Carried out Before 2008 May or After 2009 January
The Swift database includes a number of observations of LBAS blazars that were carried out outside the period that we consider useful to build our quasi-simultaneous SED. These measurements are particularly important for the case of blazars that have never previously been observed by any X-ray astronomy satellite and were below the detection threshold of the ROSAT all-sky survey. When these Swift observations have been analyzed and published by other authors we use the flux intensities reported in the literature, with particular reference to the latest online version of the BZcat catalog.94 For the cases where the Swift results have not yet appeared in the literature we list in Column 8 of Table 1 the X-ray fluxes estimated from the standard pipeline processing that is run at ASDC on all Swift XRT data shortly after they are added to the archive. This ASDC processing makes use of the "xrtpipeline" task of the XRTDAS package that is run after applying very tight data screening criteria, e.g., a CCD temperature lower than −50°C (instead of the standard limit of −47°C), thus ensuring a very effective background reduction. The calibrated and cleaned PC mode event files produced are then analyzed with the XIMAGE package v.4.4.1 and the point sources present in each XRT field are searched using the XIMAGE detection algorithm. For each source the net counts are corrected to account for CCD defects, effective exposure and vignetting using the exposure maps and a PSF correction. The count rates are finally converted into fluxes in the 0.1–2.4 keV band assuming a power-law spectral model with energy slope of 0.9 and low-energy absorption due to Galactic NH.
3.3. Other Multi-frequency Data
In order to improve the quality of our SED we complemented the Fermi and Swift quasi-simultaneous data with other multi-frequency flux measurements obtained from a number of on-going programs from ground- and space-based observatories. In the following sections, we describe each program and the corresponding data analysis.
3.3.1. Effelsberg Radio Observations
Quasi-simultaneous radio data for 25 sources of the first Fermi bright source catalog were obtained within a Fermi -related monthly broadband monitoring program including the Effelsberg 100 m radio telescope of the MPIfR (F-GAMMA project; Fuhrmann et al. 2007; Angelakis et al. 2009). From this program, radio spectra covering the frequency range 2.6–42 GHz were selected to be within the time period 2008 August 4 to 2008 October 31, i.e., quasi-simultaneous to the Fermi and Swift observations presented in Sections 3.1 and 3.2.
The Effelsberg observations were conducted with cross-scans in azimuth/elevation with the number of sub-scans matching the source brightness at the given frequencies. The individual spectra were measured quasi-simultaneously within ⩽40 minutes rapidly switching between the various secondary focus receivers. The data reduction was done applying standard procedures and post-observational corrections including (1) opacity correction, (2) pointing off-set correction, (3) gain correction, and (4) sensitivity correction (see Fuhrmann et al. 2008; Angelakis et al. 2009, for details). The sensitivity correction was done with reference to standard calibrators (e.g., 3C 286) and the measured antenna temperatures were linked to the absolute flux-density scale (Baars et al. 1977; Ott et al. 1994). The precision ranges between ≲1% to a few percent.
The results are reported in Table 5 where Column 1 gives the source name, Column 2 gives the observation date, Column 3 gives the frequency, and Column 4 gives the flux density in units of Jansky.
Table 5. Effelsberg Radio Data
Source Name | Observation Date | Frequency (GHz) | Flux Density (Jy) |
---|---|---|---|
0FGL | |||
(1) | (2) | (3) | (4) |
J0222.6+4302 | 2008 Aug 8 | 4.85 | 1.434 |
2008 Aug 8 | 8.35 | 1.247 | |
2008 Aug 8 | 10.45 | 1.159 | |
2008 Aug 8 | 14.60 | 1.087 | |
2008 Aug 8 | 23.05 | 1.086 | |
J0238.4+2855 | 2008 Sep 17 | 2.64 | 3.221 |
2008 Sep 17 | 4.85 | 3.609 | |
2008 Sep 17 | 8.35 | 3.614 | |
2008 Sep 17 | 10.45 | 3.495 | |
2008 Sep 17 | 14.60 | 3.331 | |
2008 Sep 17 | 23.05 | 3.124 | |
2008 Sep 17 | 42.00 | 2.960 | |
J0238.6+1636 | 2008 Sep 17 | 2.64 | 2.174 |
2008 Sep 17 | 4.85 | 3.235 | |
2008 Sep 17 | 8.35 | 4.102 | |
2008 Sep 17 | 10.45 | 4.295 | |
2008 Sep 17 | 14.60 | 4.450 | |
2008 Sep 17 | 23.05 | 4.569 | |
2008 Sep 17 | 42.00 | 5.030 | |
J0423.1-0112 | 2008 Oct 18 | 2.64 | 2.851 |
2008 Oct 18 | 4.85 | 3.397 | |
2008 Oct 18 | 8.35 | 3.726 | |
2008 Oct 18 | 10.45 | 3.930 | |
2008 Oct 18 | 14.60 | 4.154 | |
2008 Oct 18 | 23.05 | 4.057 | |
2008 Oct 18 | 32.00 | 3.769 | |
2008 Oct 18 | 42.00 | 3.748 | |
J0507.9+6739 | 2008 Nov 9 | 2.64 | 0.038 |
2008 Nov 9 | 4.85 | 0.035 | |
2008 Nov 9 | 8.35 | 0.030 | |
J0531.0+1331 | 2008 Dec 6 | 2.64 | 3.945 |
2008 Dec 6 | 4.85 | 4.052 | |
2008 Dec 6 | 8.35 | 3.646 | |
2008 Dec 6 | 10.45 | 3.459 | |
2008 Dec 6 | 14.60 | 3.188 | |
2008 Dec 6 | 23.05 | 2.553 | |
2008 Dec 6 | 32.00 | 2.281 | |
J0722.0+7120 | 2008 Sep 17 | 2.64 | 1.000 |
2008 Sep 17 | 4.85 | 1.110 | |
2008 Sep 17 | 8.35 | 1.408 | |
2008 Sep 17 | 10.45 | 1.544 | |
2008 Sep 17 | 14.60 | 1.744 | |
2008 Sep 17 | 23.05 | 1.928 | |
2008 Sep 17 | 42.00 | 1.833 | |
J0855.4+2009 | 2008 Oct 18 | 2.64 | 1.373 |
2008 Oct 18 | 4.85 | 1.786 | |
2008 Oct 18 | 8.35 | 2.333 | |
2008 Oct 18 | 10.45 | 2.531 | |
2008 Oct 18 | 14.60 | 2.815 | |
2008 Oct 18 | 23.05 | 3.072 | |
2008 Oct 18 | 32.00 | 2.828 | |
2008 Oct 18 | 42.00 | 2.740 | |
J1104.5+3811 | 2008 Sep 18 | 4.85 | 0.600 |
2008 Sep 18 | 8.35 | 0.499 | |
2008 Sep 18 | 10.45 | 0.468 | |
2008 Sep 18 | 14.60 | 0.428 | |
J1159.2+2912 | 2008 Sep 18 | 4.85 | 1.705 |
2008 Sep 18 | 8.35 | 2.386 | |
2008 Sep 18 | 10.45 | 2.663 | |
2008 Sep 18 | 14.60 | 2.831 | |
2008 Sep 18 | 42.00 | 2.661 | |
J1221.7+2814 | 2008 Oct 18 | 4.85 | 0.486 |
2008 Oct 18 | 8.35 | 0.458 | |
2008 Oct 18 | 10.45 | 0.440 | |
2008 Oct 18 | 14.60 | 0.412 | |
J1229.1+0202 | 2008 Sep 18 | 4.85 | 38.557 |
2008 Sep 18 | 8.35 | 35.822 | |
2008 Sep 18 | 10.45 | 34.332 | |
2008 Sep 18 | 14.60 | 30.181 | |
2008 Sep 18 | 23.05 | 24.733 | |
2008 Sep 18 | 42.00 | 18.097 | |
J1256.1-0547 | 2008 Oct 18 | 2.64 | 10.136 |
2008 Oct 18 | 4.85 | 11.535 | |
2008 Oct 18 | 8.35 | 13.974 | |
2008 Oct 18 | 10.45 | 15.263 | |
2008 Oct 18 | 14.60 | 16.560 | |
2008 Oct 18 | 23.05 | 18.230 | |
2008 Oct 18 | 32.00 | 16.895 | |
2008 Oct 18 | 42.00 | 15.287 | |
J1310.6+3220 | 2008 Sep 16 | 2.64 | 0.863 |
2008 Sep 16 | 4.85 | 0.915 | |
2008 Sep 16 | 8.35 | 1.272 | |
2008 Sep 16 | 10.45 | 1.472 | |
2008 Sep 16 | 14.60 | 1.796 | |
2008 Sep 16 | 23.05 | 2.218 | |
2008 Sep 16 | 42.00 | 2.648 | |
J1504.3+1030 | 2008 Sep 16 | 2.64 | 1.468 |
2008 Sep 16 | 4.85 | 1.391 | |
2008 Sep 16 | 8.35 | 1.486 | |
2008 Sep 16 | 10.45 | 1.582 | |
2008 Sep 16 | 14.60 | 1.815 | |
2008 Sep 16 | 23.05 | 2.007 | |
2008 Sep 16 | 42.00 | 2.231 | |
J1512.7-0905 | 2009 Jan 25 | 2.64 | 2.346 |
2009 Jan 25 | 4.85 | 2.371 | |
2009 Jan 25 | 8.35 | 2.206 | |
2009 Jan 25 | 10.45 | 2.164 | |
2009 Jan 25 | 14.60 | 2.065 | |
J1653.9+3946 | 2008 Aug 23 | 2.64 | 1.536 |
2008 Aug 23 | 4.85 | 1.465 | |
2008 Aug 23 | 8.35 | 1.345 | |
2008 Aug 23 | 10.45 | 1.278 | |
2008 Aug 23 | 14.60 | 1.195 | |
2008 Aug 23 | 23.05 | 1.056 | |
J1751.5+0935 | 2009 Jan 25 | 2.64 | 2.999 |
2009 Jan 25 | 4.85 | 3.880 | |
2009 Jan 25 | 8.35 | 5.093 | |
2009 Jan 25 | 10.45 | 5.298 | |
2009 Jan 25 | 14.60 | 6.265 | |
2009 Jan 25 | 23.05 | 6.722 | |
J1719.1+1744 | 2009 Jan 25 | 2.64 | 0.670 |
2009 Jan 25 | 4.85 | 0.675 | |
2009 Jan 25 | 8.35 | 0.626 | |
2009 Jan 25 | 10.45 | 0.599 | |
2009 Jan 25 | 14.60 | 0.599 | |
2009 Jan 25 | 32.00 | 0.516 | |
J2000.2+6506 | 2008 Nov 8 | 4.85 | 0.239 |
2008 Nov 8 | 8.35 | 0.230 | |
2008 Nov 8 | 10.45 | 0.217 | |
J2143.2+1741 | 2009 Jan 25 | 2.64 | 0.639 |
2009 Jan 25 | 4.85 | 0.683 | |
2009 Jan 25 | 10.45 | 0.701 | |
2009 Jan 25 | 14.60 | 0.740 | |
2009 Jan 25 | 32.00 | 0.801 | |
J2158.8-3014 | 2008 Sep 16 | 2.64 | 0.619 |
2008 Sep 16 | 4.85 | 0.592 | |
2008 Sep 16 | 8.35 | 0.560 | |
2008 Sep 16 | 10.45 | 0.560 | |
2008 Sep 16 | 14.60 | 0.548 | |
2008 Sep 16 | 32.00 | 0.715 | |
J2202.4+4217 | 2008 Sep 16 | 2.64 | 2.117 |
2008 Sep 16 | 4.85 | 2.365 | |
2008 Sep 16 | 8.35 | 2.461 | |
2008 Sep 16 | 10.45 | 2.440 | |
2008 Sep 16 | 14.60 | 2.446 | |
2008 Sep 16 | 23.05 | 2.373 | |
2008 Sep 16 | 42.00 | 2.393 | |
J2254.0+1609 | 2008 Sep 17 | 2.64 | 11.304 |
2008 Sep 17 | 4.85 | 9.493 | |
2008 Sep 17 | 8.35 | 10.595 | |
2008 Sep 17 | 10.45 | 11.945 | |
2008 Sep 17 | 14.60 | 14.837 | |
2008 Sep 17 | 23.05 | 20.564 | |
2008 Sep 17 | 42.00 | 29.924 |
3.3.2. OVRO Radio Data
Quasi-simultaneous 15 GHz observations of 24 Fermi LBAS sources were made using the Owens Valley Radio Observatory (OVRO) 40 m telescope. These observations were made as part of an ongoing Fermi -LAT blazar monitoring program. In this program, all 1158 CGRaBS blazars north of decl. −20° have been observed approximately twice per week or more frequently since 2007 June (Healey et al. 2008).
The OVRO flux densities are measured in a single 3 GHz wide band centered at 15 GHz. Observations were performed using azimuth double switching as described in Readhead et al. (1989), which removes much atmospheric and ground interference. The relative uncertainties in flux density result from a 5 mJy typical thermal uncertainty in quadrature with a 1.6% systematic uncertainty. The absolute flux density scale is calibrated to about 5% via observations of the steady calibrator 3C 286, using the (Baars et al. 1977) model.
For each source, the maximum and minimum observed 15 GHz flux densities during the 2008 August 4 to October 31 period were included in the quasi-simultaneous SED. The included OVRO 40 m observations are summarized in Table 6. Column 1 lists the 0FGL source name. Columns 2 and 4 list the dates of the observed maximum and minimum. Columns 3 and 5 list the measured maximum and flux density in Jansky, including the 5% absolute calibration uncertainty in the quoted error.
Table 6. OVRO Radio Data (15 GHz)
Name | Date of Max. | Max. Flux Density | Date of Min. | Min. Flux Density |
---|---|---|---|---|
0FGL | (Jy) | (Jy) | ||
(1) | (2) | (3) | (4) | (5) |
J0050.5-0928 | 2008 Oct 23 | 1.079 ± 0.057 | 2008 Dec 19 | 1.761 ± 0.092 |
J0137.1+4751 | 2008 Aug 16 | 3.05 ± 0.16 | 2008 Oct 24 | 3.73 ± 0.20 |
J0222.6+4302 | 2008 Dec 20 | 0.861 ± 0.045 | 2008 Aug 16 | 1.070 ± 0.056 |
J0238.4+2855 | 2008 Oct 22 | 2.99 ± 0.16 | 2008 Aug 30 | 3.34 ± 0.18 |
J0423.1-0112 | 2008 Nov 4 | 3.90 ± 0.20 | 2008 Nov 19 | 4.40 ± 0.23 |
J0531.0+1331 | 2008 Aug 23 | 2.87 ± 0.15 | 2008 Nov 5 | 3.26 ± 0.17 |
J0722.0+7120 | 2008 Dec 6 | 1.511 ± 0.079 | 2008 Aug 26 | 3.16 ± 0.17 |
J0855.4+2009 | 2008 Nov 12 | 2.37 ± 0.13 | 2008 Dec 24 | 3.21 ± 0.17 |
J1015.2+4927 | 2008 Aug 8 | 0.246 ± 0.014 | 2008 Dec 6 | 0.286 ± 0.016 |
J1057.8+0138 | 2008 Oct 29 | 4.26 ± 0.22 | 2008 Dec 23 | 4.63 ± 0.24 |
J1104.5+3811 | 2008 Aug 27 | 0.424 ± 0.023 | 2008 Dec 14 | 0.477 ± 0.025 |
J1159.2+2912 | 2008 Aug 14 | 2.48 ± 0.13 | 2008 Dec 12 | 3.52 ± 0.19 |
J1221.7+2814 | 2008 Aug 20 | 0.382 ± 0.021 | 2008 Aug 18 | 0.425 ± 0.023 |
J1229.1+0202 | 2008 Dec 14 | 27.3 ± 1.4 | 2008 Aug 11 | 30.6 ± 1.6 |
J1248.7+5811 | 2008 Aug 22 | 0.149 ± 0.010 | 2008 Nov 7 | 0.172 ± 0.010 |
J1256.1-0547 | 2008 Oct 18 | 16.48 ± 0.87 | 2008 Aug 12 | 17.82 ± 0.94 |
J1310.6+3220 | 2008 Aug 10 | 1.613 ± 0.085 | 2008 Nov 16 | 1.819 ± 0.095 |
J1504.4+1030 | 2008 Sep 2 | 1.667 ± 0.088 | 2008 Dec 23 | 2.40 ± 0.13 |
J1522.2+3143 | 2008 Nov 10 | 0.333 ± 0.018 | 2008 Aug 14 | 0.502 ± 0.027 |
J1653.9+3946 | 2008 Nov 11 | 1.002 ± 0.053 | 2008 Dec 5 | 1.185 ± 0.062 |
J1751.5+0935 | 2008 Aug 8 | 4.48 ± 0.24 | 2008 Dec 21 | 7.12 ± 0.37 |
J1849.4+6706 | 2008 Nov 2 | 1.705 ± 0.090 | 2008 Dec 13 | 2.41 ± 0.13 |
J2000.2+6506 | 2008 Aug 18 | 0.167 ± 0.010 | 2008 Dec 5 | 0.226 ± 0.012 |
J2327.3+0947 | 2008 Aug 9 | 1.494 ± 0.078 | 2008 Dec 17 | 1.95 ± 0.10 |
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3.3.3. RATAN-600 1–22 GHz Radio Observations
Among the 48 objects for which we present Swift and Fermi simultaneous SED, 32 were observed between 2008 September 10 and October 3 with the 600 m ring radio telescope RATAN-600 (Korolkov & Parijskij 1979) of the Special Astrophysical Observatory, Russian Academy of Sciences, located in Zelenchukskaya, Russia. These observations, which produced 1–22 GHz instantaneous radio spectra, are part of a long-term program (e.g., Kovalev et al. 2002) to monitor continuum spectra of active galactic nuclei (AGNs) with a strong parsec-scale component of radio emission. The current list contains a complete sample of more than 600 AGNs with decl. δ> − 30° and correlated VLBI flux density greater than 400 mJy selected from Kovalev et al. (2007).
Broadband radio continuum spectra were measured quasi-simultaneously in a transit mode at six different bands with the following central frequencies (and frequency bands): 0.95 GHz (0.03 GHz), 2.3 GHz (0.25 GHz), 4.8 GHz (0.6 GHz), 7.7 GHz (1.0 GHz), 11.2 GHz (1.4 GHz), and 21.7 GHz (2.5 GHz). Each source was observed in the upper culmination with an unmoved antenna due to the Earth rotation collecting a multi-frequency source scan within several minutes. Details on the method of observation, data processing, and amplitude calibration are described in Kovalev et al. (1999). Presented data were collected using the Southern ring sector with the Flat reflector of RATAN-600. The spectrum of every object was measured, typically, 3 times during the observing set. Averaged flux density spectra used in our SED are presented in Table 7 where Column 1 gives the source name, Column 2 gives the frequency of observations, and Column 3 gives the radio flux density in units of Jansky. During recent years, the radio frequency interference became stronger at the two lowest frequency bands, 1 and 2.3 GHz. This results in higher measurement errors and sometimes even loss of data, especially at the lowest frequency band. Bad weather conditions resulted in elevated errors at 22 GHz in a few cases.
Table 7. RATAN-600 Flux Density Measurements in 2008 September 10–October 3
Source Name | Central Frequency | Flux Density |
---|---|---|
0FGL | (GHz) | (Jy) |
(1) | (2) | (3) |
0FGL J0050.5 − 0928 | 21.7 | 0.98 ± 0.06 |
11.2 | 1.10 ± 0.04 | |
7.7 | 1.09 ± 0.03 | |
4.8 | 0.97 ± 0.01 | |
2.3 | 0.95 ± 0.11 | |
1.0 | 0.91 ± 0.15 | |
0FGL J0137.1+4751 | 21.7 | 3.43 ± 0.06 |
11.2 | 3.75 ± 0.07 | |
7.7 | 3.61 ± 0.06 | |
4.8 | 3.00 ± 0.04 | |
2.3 | 2.06 ± 0.31 | |
0FGL J0222.6+4302 | 21.7 | 0.88 ± 0.06 |
11.2 | 1.13 ± 0.02 | |
7.7 | 1.32 ± 0.03 | |
4.8 | 1.19 ± 0.08 | |
0FGL J0238.4+2855 | 21.7 | 2.69 ± 0.17 |
11.2 | 3.10 ± 0.07 | |
7.7 | 3.44 ± 0.07 | |
4.8 | 3.50 ± 0.05 | |
2.3 | 3.51 ± 0.27 | |
1.0 | 3.75 ± 0.55 | |
0FGL J0238.6+1636 | 21.7 | 3.76 ± 0.20 |
11.2 | 3.96 ± 0.14 | |
7.7 | 3.70 ± 0.11 | |
4.8 | 3.11 ± 0.12 | |
2.3 | 2.09 ± 0.10 | |
1.0 | 1.15 ± 0.19 | |
0FGL J0349.8 − 2102 | 21.7 | 1.10 ± 0.10 |
11.2 | 0.79 ± 0.03 | |
7.7 | 0.82 ± 0.07 | |
4.8 | 0.61 ± 0.11 | |
2.3 | 0.28 ± 0.11 | |
1.0 | 0.18 ± 0.03 | |
0FGL J0423.1 − 0112 | 21.7 | 3.34 ± 0.05 |
11.2 | 3.52 ± 0.04 | |
7.7 | 3.44 ± 0.07 | |
4.8 | 3.42 ± 0.08 | |
2.3 | 2.63 ± 0.20 | |
0FGL J0457.1 − 2325 | 21.7 | 1.98 ± 0.09 |
11.2 | 3.02 ± 0.16 | |
7.7 | 3.02 ± 0.20 | |
4.8 | 2.28 ± 0.11 | |
2.3 | 1.61 ± 0.27 | |
1.0 | 1.50 ± 0.15 | |
0FGL J0531.0+1331 | 21.7 | 2.37 ± 0.06 |
11.2 | 2.95 ± 0.04 | |
7.7 | 3.10 ± 0.04 | |
4.8 | 3.33 ± 0.08 | |
2.3 | 2.99 ± 0.11 | |
1.0 | 1.35 ± 0.19 | |
0FGL J0722.0+7120 | 21.7 | 2.26 ± 0.16 |
11.2 | 2.23 ± 0.06 | |
7.7 | 1.81 ± 0.07 | |
4.8 | 1.43 ± 0.10 | |
2.3 | 1.05 ± 0.18 | |
0FGL J0730.4 − 1142 | 21.7 | 5.99 ± 0.23 |
11.2 | 7.55 ± 0.12 | |
7.7 | 7.33 ± 0.09 | |
4.8 | 5.64 ± 0.35 | |
2.3 | 3.54 ± 0.25 | |
0FGL J0855.4+2009 | 21.7 | 2.81 ± 0.19 |
11.2 | 2.73 ± 0.04 | |
7.7 | 2.45 ± 0.04 | |
4.8 | 1.88 ± 0.17 | |
2.3 | 1.38 ± 0.16 | |
0FGL J0921.2+4437 | 21.7 | 2.12 ± 0.10 |
11.2 | 1.69 ± 0.03 | |
7.7 | 1.31 ± 0.24 | |
4.8 | 1.13 ± 0.13 | |
2.3 | 1.22 ± 0.17 | |
0FGL J1057.8+0138 | 21.7 | 3.67 ± 0.13 |
11.2 | 3.98 ± 0.24 | |
7.7 | 3.56 ± 0.05 | |
4.8 | 3.07 ± 0.09 | |
2.3 | 2.89 ± 0.13 | |
0FGL J1104.5+3811 | 21.7 | 0.53 ± 0.14 |
11.2 | 0.43 ± 0.03 | |
7.7 | 0.47 ± 0.04 | |
4.8 | 0.49 ± 0.11 | |
2.3 | 0.44 ± 0.13 | |
1.0 | 0.38 ± 0.06 | |
0FGL J1159.2+2912 | 21.7 | 2.93 ± 0.15 |
11.2 | 2.85 ± 0.10 | |
7.7 | 2.45 ± 0.04 | |
4.8 | 1.66 ± 0.05 | |
2.3 | 1.02 ± 0.14 | |
0FGL J1229.1+0202 | 21.7 | 21.35 ± 0.61 |
11.2 | 32.51 ± 0.43 | |
7.7 | 36.40 ± 0.37 | |
4.8 | 37.81 ± 2.06 | |
2.3 | 48.10 ± 0.97 | |
0FGL J1256.1 − 0547 | 21.7 | 16.44 ± 0.62 |
11.2 | 15.09 ± 1.36 | |
7.7 | 14.72 ± 0.28 | |
4.8 | 11.76 ± 1.52 | |
2.3 | 10.31 ± 0.58 | |
0FGL J1310.6+3220 | 21.7 | 1.68 ± 0.28 |
11.2 | 1.49 ± 0.01 | |
7.7 | 1.25 ± 0.07 | |
4.8 | 0.91 ± 0.04 | |
2.3 | 0.81 ± 0.13 | |
0FGL J1457.6 − 3538 | 21.7 | 1.18 ± 0.18 |
11.2 | 1.20 ± 0.04 | |
7.7 | 1.25 ± 0.03 | |
4.8 | 0.89 ± 0.03 | |
2.3 | 0.83 ± 0.08 | |
1.0 | 1.02 ± 0.15 | |
0FGL J1504.3+1030 | 21.7 | 1.75 ± 0.14 |
11.2 | 1.54 ± 0.05 | |
7.7 | 1.41 ± 0.03 | |
4.8 | 1.35 ± 0.07 | |
2.3 | 1.52 ± 0.10 | |
1.0 | 1.54 ± 0.10 | |
0FGL J1512.7 − 0905 | 21.7 | 2.75 ± 0.26 |
11.2 | 3.34 ± 0.25 | |
7.7 | 3.23 ± 0.12 | |
4.8 | 2.58 ± 0.21 | |
2.3 | 2.16 ± 0.19 | |
0FGL J1522.2+3143 | 21.7 | 0.34 ± 0.07 |
11.2 | 0.47 ± 0.02 | |
7.7 | 0.55 ± 0.05 | |
4.8 | 0.53 ± 0.03 | |
2.3 | 0.65 ± 0.12 | |
0FGL J1543.1+6130 | 11.2 | 0.11 ± 0.02 |
7.7 | 0.09 ± 0.04 | |
4.8 | 0.06 ± 0.03 | |
0FGL J1653.9+3946 | 21.7 | 0.94 ± 0.09 |
11.2 | 1.31 ± 0.03 | |
7.7 | 1.44 ± 0.04 | |
4.8 | 1.29 ± 0.15 | |
2.3 | 1.54 ± 0.14 | |
1.0 | 1.89 ± 0.23 | |
0FGL J1719.3+1746 | 21.7 | 0.56 ± 0.13 |
11.2 | 0.60 ± 0.05 | |
7.7 | 0.66 ± 0.02 | |
4.8 | 0.62 ± 0.04 | |
2.3 | 0.55 ± 0.10 | |
1.0 | 0.37 ± 0.09 | |
0FGL J1751.5+0935 | 21.7 | 5.36 ± 0.23 |
11.2 | 4.34 ± 0.07 | |
7.7 | 3.06 ± 0.10 | |
4.8 | 1.94 ± 0.08 | |
2.3 | 1.46 ± 0.12 | |
0FGL J2000.2+6506 | 11.2 | 0.23 ± 0.03 |
7.7 | 0.28 ± 0.02 | |
4.8 | 0.35 ± 0.07 | |
0FGL J2143.2+1741 | 21.7 | 0.58 ± 0.09 |
11.2 | 0.60 ± 0.02 | |
7.7 | 0.58 ± 0.02 | |
4.8 | 0.51 ± 0.04 | |
2.3 | 0.49 ± 0.08 | |
0FGL J2158.8 − 3014 | 11.2 | 0.56 ± 0.03 |
7.7 | 0.70 ± 0.04 | |
4.8 | 0.59 ± 0.03 | |
2.3 | 0.69 ± 0.06 | |
1.0 | 0.79 ± 0.20 | |
0FGL J2202.4+4217 | 21.7 | 2.30 ± 0.11 |
11.2 | 2.69 ± 0.03 | |
7.7 | 2.77 ± 0.03 | |
4.8 | 2.25 ± 0.07 | |
2.3 | 1.95 ± 0.12 | |
1.0 | 1.80 ± 0.22 | |
0FGL J2254.0+1609 | 11.2 | 11.45 ± 0.10 |
7.7 | 9.68 ± 0.06 | |
4.8 | 9.25 ± 0.13 | |
2.3 | 12.07 ± 0.10 | |
1.0 | 15.57 ± 1.05 | |
0FGL J2327.3+0947 | 21.7 | 1.35 ± 0.10 |
11.2 | 1.31 ± 0.06 | |
7.7 | 1.21 ± 0.08 | |
4.8 | 1.12 ± 0.07 | |
2.3 | 0.72 ± 0.06 | |
1.0 | 0.71 ± 0.09 |
3.3.4. Radio, mm, NIR and Optical Data from the GASP–WEBT Collaboration
The GLAST–AGILE Support Program (GASP) originated from the Whole Earth Blazar Telescope95 (WEBT; see e.g., Villata et al. 2007; Raiteri et al. 2008a)) and started its operation in 2007 September (see Villata et al. 2008), with the aim of performing long-term optical-to-radio monitoring of 28 γ-loud blazars, to compare the low-energy flux behavior with the behavior observed at γ-ray energies.
In the period considered in this work, the GASP carried out ∼3000 optical (R band) observations of 19 LBAS blazars, while ∼700 near-IR (JHK, Campo Imperatore), and ∼600 microwave (230 and 345 GHz, SMA) and radio data (5–43 GHz, Medicina, Noto, UMRAO) observations were taken on the same sources.
The optical and near-IR magnitudes were de-reddened by assuming the Galactic extinction in the B band from Schlegel et al. (1998) and deriving the extinction in the other bands according to Cardelli et al. (1989). The conversion to fluxes was performed adopting the zero-mag fluxes by Bessel et al. (1998).
In the SED plots, we report the average, maximum, and minimum values at each observed frequency in the period 2008 August 4–October 31.96
Table 8 reports the plotted values directly as log(νFν): the average, maximum, and minimum values are shown in Columns 3, 4, and 5, respectively. Column 6 displays the number of data available in the period. When the number of data available is reported as "0" this indicates that the data given in the table and shown in the SED plots are not strictly inside the period (this happens for ON 231 and 3C 279 in the optical, and for 3C 273 in both the optical and near-IR, because of solar conjunction), but come from immediately outside and, due to the smoothness of the light curve, they can represent the state in between. Note that Columns 4 and 5 report the error bar extremes instead of maximum and minimum values.
Table 8. GASP–WEBT Data
Name | log (ν) | log (νFν) | log (νFν) | log (νFν) | Ndata |
---|---|---|---|---|---|
(average) | (max) | min | |||
(1) | (2) | (3) | (4) | (5) | (6) |
J0222.6+4302 | 14.670 | −10.446 | −10.246 | −10.668 | 521 |
14.390 | −10.467 | −10.300 | −10.638 | 21 | |
14.265 | −10.477 | −10.324 | −10.643 | 21 | |
14.136 | −10.496 | −10.365 | −10.661 | 21 | |
10.633 | −12.394 | −12.371 | −12.417 | 2 | |
10.342 | −12.694 | −12.623 | −12.778 | 2 | |
10.161 | −12.850 | −12.820 | −12.900 | 3 | |
9.903 | −13.011 | −13.007 | −13.017 | 4 | |
J0238.6+1636 | 14.670 | −10.554 | −10.011 | −11.366 | 619 |
14.390 | −10.439 | −10.007 | −11.145 | 64 | |
14.265 | −10.401 | −10.000 | −11.058 | 62 | |
14.136 | −10.383 | −9.983 | −10.990 | 63 | |
11.538 | −10.997 | −10.893 | −11.038 | 7 | |
11.362 | −11.056 | −10.937 | −11.188 | 13 | |
10.633 | −11.640 | −11.618 | −11.663 | 2 | |
10.342 | −12.101 | −12.008 | −12.220 | 2 | |
10.161 | −12.204 | −12.049 | −12.363 | 22 | |
9.903 | −12.432 | −12.302 | −12.614 | 11 | |
9.699 | −12.725 | −12.576 | −12.888 | 8 | |
J0423.1 − 0112 | 14.670 | −11.428 | −11.332 | −11.486 | 3 |
14.390 | −11.307 | −11.285 | −11.327 | 6 | |
14.265 | −11.251 | −11.197 | −11.296 | 6 | |
14.136 | −11.162 | −11.128 | −11.187 | 6 | |
11.538 | −11.253 | −11.195 | −11.346 | 8 | |
11.362 | −11.294 | −11.249 | −11.368 | 16 | |
10.633 | −11.761 | −11.738 | −11.785 | 2 | |
10.342 | −12.079 | −12.069 | −12.089 | 2 | |
10.161 | −12.239 | −12.210 | −12.281 | 20 | |
9.903 | −12.496 | −12.434 | −12.543 | 8 | |
9.699 | −12.793 | −12.784 | −12.803 | 1 | |
J0531.0+1331 | 14.670 | −11.646 | −11.624 | −11.669 | 2 |
14.390 | −11.866 | −11.705 | −11.997 | 7 | |
14.265 | −11.861 | −11.682 | −12.057 | 7 | |
14.136 | −11.918 | −11.680 | −12.115 | 6 | |
11.538 | −11.468 | −11.417 | −11.538 | 6 | |
11.362 | −11.487 | −11.437 | −11.552 | 11 | |
10.633 | −11.887 | −11.865 | −11.911 | 2 | |
10.342 | −12.146 | −12.092 | −12.207 | 1 | |
10.161 | −12.357 | −12.319 | −12.383 | 12 | |
9.903 | −12.566 | −12.560 | −12.571 | 2 | |
9.699 | −12.744 | −12.726 | −12.767 | 3 | |
J0722.0+7120 | 14.670 | −10.017 | −9.809 | −10.240 | 56 |
14.390 | −10.038 | −9.902 | −10.188 | 16 | |
14.265 | −10.035 | −9.908 | −10.181 | 15 | |
14.136 | −10.012 | −9.898 | −10.148 | 15 | |
11.538 | −11.293 | −11.195 | −11.421 | 1 | |
11.362 | −11.228 | −11.090 | −11.402 | 6 | |
10.633 | −11.876 | −11.868 | −11.883 | 2 | |
10.342 | −12.237 | −12.202 | −12.276 | 2 | |
10.161 | −12.550 | −12.395 | −12.669 | 10 | |
9.903 | −12.920 | −12.797 | −13.040 | 7 | |
9.699 | −13.220 | −13.155 | −13.328 | 7 | |
J0855.4+2009 | 14.670 | −10.379 | −10.215 | −10.485 | 13 |
14.390 | −10.222 | −10.108 | −10.293 | 4 | |
14.265 | −10.166 | −10.059 | −10.228 | 4 | |
14.136 | −10.124 | −10.035 | −10.177 | 5 | |
11.362 | −11.216 | −11.145 | −11.271 | 6 | |
10.633 | −11.885 | −11.877 | −11.892 | 2 | |
10.342 | −12.188 | −12.149 | −12.230 | 2 | |
10.161 | −12.410 | −12.372 | −12.446 | 9 | |
9.903 | −12.707 | −12.672 | −12.731 | 4 | |
9.699 | −13.089 | −13.021 | −13.170 | 2 | |
J1104.5+3811 | 14.670 | −10.100 | −10.078 | −10.123 | 2 |
11.362 | −12.180 | −12.089 | −12.296 | 0 | |
10.161 | −13.207 | −13.138 | −13.274 | 8 | |
9.903 | −13.323 | −13.148 | −13.665 | 7 | |
9.699 | −13.485 | −13.438 | −13.538 | 2 | |
J1159.2+2912 | 11.362 | −11.396 | −11.373 | −11.419 | 1 |
10.633 | −11.850 | −11.842 | −11.858 | 2 | |
10.342 | −12.096 | −11.972 | −12.271 | 2 | |
10.161 | −12.392 | −12.329 | −12.476 | 17 | |
9.903 | −12.753 | −12.697 | −12.789 | 6 | |
9.699 | −13.141 | −13.121 | −13.161 | 2 | |
J1221.7+2814 | 14.670 | −10.621 | −10.604 | −10.638 | 0 |
10.633 | −12.716 | −12.685 | −12.749 | 1 | |
10.342 | −13.017 | −12.881 | −13.217 | 1 | |
10.161 | −13.252 | −13.231 | −13.274 | 1 | |
9.903 | −13.492 | −13.423 | −13.573 | 2 | |
9.699 | −13.740 | −13.611 | −14.046 | 3 | |
J1229.1+0202 | 14.670 | −9.837 | −9.828 | −9.846 | 0 |
14.390 | −10.038 | −10.036 | −10.040 | 0 | |
14.265 | −10.031 | −10.029 | −10.033 | 0 | |
14.136 | −9.894 | −9.892 | −9.896 | 0 | |
11.538 | −10.521 | −10.408 | −10.673 | 0 | |
11.362 | −10.669 | −10.508 | −10.792 | 3 | |
10.633 | −11.148 | −11.129 | −11.168 | 2 | |
10.342 | −11.230 | −11.224 | −11.236 | 2 | |
10.161 | −11.360 | −11.340 | −11.374 | 12 | |
9.903 | −11.541 | −11.521 | −11.556 | 9 | |
9.699 | −11.721 | −11.719 | −11.724 | 4 | |
J1256.1 − 0547 | 14.670 | −11.006 | −10.788 | −11.466 | 0 |
11.362 | −10.691 | −10.663 | −10.705 | 4 | |
10.633 | −11.077 | −11.022 | −11.140 | 2 | |
10.342 | −11.334 | −11.307 | −11.358 | 3 | |
10.161 | −11.618 | −11.592 | −11.670 | 8 | |
9.903 | −11.942 | −11.927 | −11.980 | 8 | |
9.699 | −12.231 | −12.221 | −12.237 | 4 | |
J1512.7 − 0905 | 14.670 | −11.363 | −11.245 | −11.451 | 21 |
14.390 | −11.376 | −11.308 | −11.450 | 3 | |
14.265 | −11.341 | −11.269 | −11.457 | 3 | |
14.136 | −11.234 | −11.201 | −11.307 | 3 | |
11.362 | −11.430 | −11.404 | −11.458 | 1 | |
10.633 | −11.935 | −11.886 | −11.991 | 2 | |
10.342 | −12.109 | −12.080 | −12.140 | 2 | |
10.161 | −12.386 | −12.305 | −12.446 | 15 | |
9.903 | −12.624 | −12.595 | −12.656 | 7 | |
9.699 | −12.880 | −12.817 | −12.921 | 6 | |
J1653.9+3946 | 14.670 | −10.105 | −10.085 | −10.121 | 7 |
14.390 | −9.973 | −9.971 | −9.976 | 6 | |
14.265 | −9.967 | −9.952 | −9.974 | 7 | |
14.136 | −10.154 | −10.149 | −10.157 | 5 | |
11.362 | −12.003 | −11.967 | −12.042 | 0 | |
10.633 | −12.459 | −12.417 | −12.506 | 1 | |
10.161 | −12.792 | −12.775 | −12.820 | 9 | |
9.903 | −12.949 | −12.898 | −12.983 | 7 | |
9.699 | −13.156 | −13.116 | −13.184 | 4 | |
J2158.8 − 3014 | 14.670 | −9.917 | −9.760 | −10.050 | 46 |
10.161 | −13.226 | −13.173 | −13.335 | 5 | |
J2202.4+4217 | 14.670 | −10.132 | −9.970 | −10.272 | 1095 |
14.390 | −10.066 | −9.920 | −10.175 | 39 | |
14.265 | −10.068 | −9.921 | −10.174 | 38 | |
14.136 | −10.108 | −9.943 | −10.212 | 34 | |
11.538 | −11.285 | −11.211 | −11.357 | 5 | |
11.362 | −11.374 | −11.260 | −11.463 | 8 | |
10.633 | −11.928 | −11.908 | −11.950 | 2 | |
10.342 | −12.162 | −12.151 | −12.172 | 2 | |
10.161 | −12.425 | −12.384 | −12.488 | 15 | |
9.903 | −12.659 | −12.568 | −12.711 | 12 | |
9.699 | −12.913 | −12.820 | −12.981 | 16 | |
J2254.0+1609 | 14.670 | −10.654 | −10.426 | −11.009 | 556 |
14.390 | −10.531 | −10.259 | −10.909 | 35 | |
14.265 | −10.475 | −10.171 | −10.901 | 34 | |
14.136 | −10.399 | −10.207 | −10.834 | 33 | |
11.538 | −10.202 | −10.107 | −10.404 | 21 | |
11.362 | −10.300 | −10.206 | −10.527 | 54 | |
10.633 | −10.931 | −10.915 | −10.947 | 2 | |
10.342 | −11.394 | −11.373 | −11.417 | 2 | |
10.161 | −11.705 | −11.662 | −11.757 | 23 | |
9.903 | −12.077 | −12.048 | −12.122 | 13 | |
9.699 | −12.322 | −12.312 | −12.333 | 16 |
The optical data of Mkn 421 have been cleaned for the contribution of the host galaxy, according to Nilsso et al. (2007). As for PKS 0235+164, we corrected the fluxes for both the photometric contribution from the southern AGN and the additional extinction due to the intervening DLA system, according to Raiteri et al. (2005); see also Raiteri et al. (2008b).
3.3.5. Mid-infrared VISIR Observations
The MIR observations were carried out from 2006 to 2008 using VISIR (Lagage et al. 2004), the ESO/VLT mid-infrared imager and spectrograph, composed of an imager and a long-slit spectrometer covering several filters in N and Q bands and mounted on Unit 3 of the VLT (Melipal). The standard "chopping and nodding" MIR observational technique was used to suppress the background dominating at these wavelengths. Secondary mirror-chopping was performed in the north–south direction with an amplitude of 16'' at a frequency of 0.25 Hz. Nodding technique, needed to compensate for chopping residuals, was chosen as parallel to the chopping and applied using telescope offsets of 16''. Because of the high thermal MIR background for ground-based observations, the detector integration time was set to 16 ms.
We performed broadband photometry in three filters, PAH1 (λ = 8.59 ± 0.42 μm), PAH2 (λ = 11.25 ± 0.59 μm), and Q2 (λ = 18.72 ± 0.88 μm) using the small field in all bands (192 × 192 and 0075 plate scale). All the observations were bracketed with standard star observations for flux calibration and PSF determination. The weather conditions were good and stable during the observations.
Raw data were reduced using the IDL reduction package (E. Pantin 2010, in preparation). The elementary images were co-added in real time to obtain chopping-corrected data, then the different nodding positions were combined to form the final image. The VISIR detector is affected by stripes randomly triggered by some abnormal high-gain pixels. A dedicated destriping method was developed to suppress them. The MIR fluxes and observation dates of all observed sources including the 1σ errors are listed in Table 9.
Table 9. Mid-infrared Photometry of Blazars Obtained with the VISIR Instrument on VLT/UT3
Source Name | Observation Date | UT | Filter | Flux | Error |
---|---|---|---|---|---|
0FGL | (mJy) | (mJy) | |||
(1) | (2) | (3) | (4) | (5) | (6) |
J0238.6+1636 | 2008 Jul 6 | 10:08 | PAH1 | 82.44 | 2.02 |
2008 Jul 7 | 09:10 | PAH1 | 108.02 | 2.03 | |
2008 Jul 7 | 09:36 | PAH2 | 155.15 | 3.59 | |
2008 Jul 7 | 09:48 | Q2 | 180.94 | 9.59 | |
J0457.0 − 2325 | 2006 Dec 1 | 12:00 | PAH2 | 67.7 | 1.8 |
2006 Dec 1 | 12:00 | Q2 | 73.0 | 5.3 | |
J1256.1 − 0547 | 2007 Jul 15 | 00:48 | PAH1 | 292.09 | 2.63 |
2007 Jul 15 | 01:13 | Q2 | 335.81 | 11.66 | |
2007 Jul 15 | 01:27 | PAH2 | 300.58 | 3.49 | |
2008 Jul 7 | 23:16 | PAH1 | 33.73 | 2.29 | |
2008 Jul 7 | 23:27 | PAH2 | 40.91 | 2.22 | |
2008 Jul 7 | 23:39 | Q2 | 106.49 | 8.25 | |
J1512.7 − 0905 | 2008 Jul 6 | 00:54 | PAH1 | 20.41 | 1.44 |
2008 Jul 6 | 01:20 | Q2 | 102.16 | 11.41 | |
2008 Jul 6 | 02:11 | PAH2 | 37.33 | 3.83 | |
J2158.8 − 3014 | 2007 Jul 15 | 09:03 | PAH1 | 295.31 | 2.44 |
2008 Jul 4 | 08:01 | PAH1 | 136.70 | 1.86 | |
2008 Jul 4 | 08:27 | Q2 | 190.70 | 12.05 | |
2008 Jul 4 | 08:51 | PAH2 | 163.61 | 2.51 | |
2008 Jul 5 | 07:21 | PAH1 | 134.01 | 3.25 | |
2008 Jul 5 | 07:33 | Q2 | 180.87 | 13.74 | |
2008 Jul 5 | 07:48 | PAH2 | 160.83 | 4.02 | |
2008 Jul 6 | 06:09 | PAH2 | 78.89 | 3.17 | |
2008 Jul 6 | 06:20 | Q2 | 93.89 | 7.66 | |
2008 Jul 6 | 06:35 | PAH1 | 70.21 | 4.73 | |
2008 Jul 6 | 07:08 | PAH1 | 160.47 | 3.31 | |
2008 Jul 6 | 07:19 | PAH2 | 201.40 | 6.03 | |
2008 Jul 6 | 07:31 | Q2 | 191.08 | 10.35 | |
2008 Jul 7 | 04:49 | PAH1 | 144.39 | 3.51 | |
2008 Jul 7 | 05:00 | PAH2 | 147.41 | 2.87 | |
2008 Jul 7 | 05:11 | Q2 | 164.30 | 10.43 |
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3.3.6. Non-simultaneous Spitzer Space Telescope Observations
The Spitzer is a 0.85 m class telescope launched on 2003 August 25. Spitzer obtains images and spectra in the spectral range between 3 and 180 μm through three instruments on board: the InfraRed Array Camera, which provides images at 3.6, 4.5, 5.8, and 8.0 μm, the Multiband Imaging Photometer for Spitzer (MIPS), which performs imaging photometry at 24, 70, and 160 μm, and the InfraRed Spectrograph which provides spectra over 5–38 μm in low (R ∼ 60–127) and high (R ∼ 600) spectral resolution mode. The Spitzer Science Archive includes MIPS observations of eight sources belonging to the LBAS sample, all of them performed earlier than three months from the start of the LBAS data taking period. From the Spitzer Archive we retrieved the post-BCD (post-basic calibrated data), that is, products generated after calibration of the individual BCD exposures. The DAOPHOT package was used for the photometric analysis, which was carried out on the post-BCD using the method of aperture photometry and subtracting the background emission. The results are reported in Table 10 where Column 1 gives the source name, Column 2 gives the observation date, Column 3 gives the log of frequency log(ν), and Column 4 gives the log of νFν.
Table 10. MIPS (Spitzer) Data
Source Name | Observation Date | log (ν) | log (νFν) |
---|---|---|---|
(1) | (2) | (3) | (4) |
J1653.9+3946 | 2004 Apr 11 | 13.097 | −11.080 |
J1229.1+0202 | 2007 Jan 15 | 13.097 | −10.121 |
2007 Jan 15 | 12.632 | −10.391 | |
2007 Jan 15 | 12.273 | −10.680 | |
2007 Jul 11 | 13.097 | −10.160 | |
2007 Jul 11 | 12.632 | −10.499 | |
J2202.4+4217 | 2006 Jul 22 | 13.097 | −10.343 |
2006 Jul 22 | 12.632 | −10.503 | |
2006 Jul 22 | 12.273 | −10.806 | |
J2158.8 − 3014 | 2004 Nov 9 | 13.097 | −10.937 |
2004 Nov 9 | 12.632 | −11.251 | |
2004 Nov 9 | 12.273 | −11.492 | |
2004 Nov 27 | 13.097 | −10.617 | |
J1256.1 − 0547 | 2007 Feb 26 | 13.097 | −10.281 |
2007 Feb 26 | 12.632 | −10.218 | |
2007 Feb 26 | 12.273 | −10.535 | |
2007 Jul 12 | 13.097 | −10.308 | |
2007 Jul 12 | 12.632 | −10.302 | |
J1221.7+2814 | 2007 Jun 6 | 13.097 | −11.210 |
2007 Jun 6 | 12.632 | −11.494 | |
2007 Jun 6 | 12.273 | −11.784 | |
2008 Jan 8 | 13.097 | −11.023 | |
2008 Jan 8 | 12.632 | −11.321 | |
2008 Jan 8 | 12.273 | −11.506 | |
J1159.2+2912 | 2005 May 14 | 13.097 | −11.023 |
2005 May 14 | 12.632 | −11.151 | |
2005 May 14 | 12.273 | −11.448 | |
2006 Apr 8 | 13.097 | −10.543 | |
2006 Apr 8 | 12.632 | −10.725 | |
2006 Apr 8 | 12.273 | −11.162 | |
J0722.0+7120 | 2006 Apr 8 | 13.097 | −10.545 |
2006 Apr 8 | 12.632 | −10.725 | |
2006 Apr 8 | 12.273 | −11.162 |
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3.3.7. AGILE γ-ray Data
The AGILE satellite, launched in 2007 April, is an Italian Space Agency (ASI) mission devoted to γ-ray astrophysics in the 30 MeV–50 GeV energy range, with simultaneous X-ray imaging in the 18–60 keV band. The AGILE instrument (Tavani et al. 2008, 2009) consists of the Silicon Tracker (ST), the X-ray detector SuperAGILE (SA), the CsI(Tl) Mini-Calorimeter (MCAL), and an anti-coincidence system (ACS). The combination of ST, MCAL and ACS forms the Gamma-Ray Imaging Detector (GRID).
The γ-ray data collected by the GRID for energies greater than 100 MeV used in this paper (blue star symbols in the SED figures) are extracted from the first AGILE catalog of high-confidence γ-ray sources detected by AGILE during the first 12 months of operations, from 2007 July 9 to 2008 June 30 (Pittori et al. 2009). The first AGILE catalog includes only high-significance sources characterized by a prominent mean γ-ray flux above 100 MeV when integrated over the total one year exposure period.
Flare detections and determination of source peak fluxes through dedicated investigation over shorter timescales are not included in the first AGILE catalog. However, it should be noted that for some blazars, such as Mkn 421 (1AGL J1104+3754) ON 231/W Comae (1AGL J1222+2851), PKS 1510-089 (1AGL J1511-0908), and 3C279 (1AGL J1256-0549), the effective AGILE exposure over the entire time period was quite low, only a few effective days, but it included target of opportunity or previously planned observations during a flaring state of the source. In such cases the AGILE observed mean γ-ray flux may be close to the source peak flux values.
The differential AGILE flux values appearing in the SED figures at fixed energy point (E = 300 MeV) have been rescaled from the mean γ-ray flux above 100 MeV, obtained with a simple power-law source model with fixed spectral index −2.1.
Table 11 reports the results where Column 1 gives the source name, Column 2 gives the AGILE observed flux, and Column 3 gives the mean exposure.
Table 11. AGILE Mean Fluxes
Name | AGILE Flux | AGILE Mean Exposure |
---|---|---|
(10−8 ph cm−2 s−1) | (108 cm2 s) | |
(1) | (2) | (3) |
0FGL J0538.8 − 4403 | 43 ± 10 | 0.81 |
0FGL J0722.0+7120 | 69 ± 9 | 1.39 |
0FGL J1104.5+3811 | 42 ± 13 | 0.51 |
0FGL J1221.7+2814 | 38 ± 11 | 0.50 |
0FGL J1229.1+0202 | 24 ± 6 | 1.98 |
0FGL J1256.1 − 0547 | 65 ± 9 | 1.98 |
0FGL J0538.8 − 4403 | 43 ± 10 | 0.81 |
0FGL J1849.4+6706 | 20 ± 4 | 5.52 |
0FGL J2254.0+1609 | 200 ± 14 | 1.16 |
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4. QUASI-SIMULTANEOUS RADIO TO γ-RAY SED OF 48 LBAS BLAZARS
In this section, we use the multi-frequency data described above to build quasi-simultaneous SED of 48 objects, in the usual log ν–log ν Fν representation. These 48 sources are a sizable subset (≈45%) of LBAS that is representative of the entire sample since they were chosen only on the basis of the availability of Swift observations carried out between 2008 May and 2009 January (which have been scheduled largely independently of Fermi results) and not on brightness level or on any other condition that could influence the shape of the SED. We checked this by verifying that the distributions of redshift, optical, X-ray, and γ-ray fluxes are all consistent with being the same in the two subsamples.
We stress that there is one important difference between γ-ray and other multi-frequency data: our Fermi data were collected over a period of three months while all other data were collected over much shorter periods (typically less than a few hours) and are not necessarily simultaneous among themselves. This is clearly a limitation as flux and spectral variability in blazars often takes place on short timescales. Such a behavior is clearly visible, in fact, in our multi-frequency data when more than one Swift observation is available (see, e.g., Figures 3, 4, 6, etc.). Since our γ-ray data have been accumulated over the relatively long period of three months, they likely represent the average of different intensity states.
The SED that we have built are shown in Figures 1–24, where the Fermi γ-ray data and the quasi-simultaneous multi-frequency measurements appear as large filled red symbols. In all the SED, we have also included non-simultaneous multi-frequency archival measurements (small open gray points) to increase the data coverage in some energy bands and to illustrate the historical range of variability at different frequencies. Archival data points have been collected using the NED (NASA/IPAC Extragalactic Database) and ASDC online services. The TeV data have been derived from the available literature as listed in Table 12.
Figures 1–24 show that in all cases the overall shape of the SED exhibit the typical broad double hump distribution, where the first bump is attributed to synchrotron radiation and the second one is likely due to one or more components related to inverse Compton emission. The dashed lines represent the best fit to the data as described in the next section.
Our SED show that there are considerable differences in the position of the peaks of the two components and on their relative peak intensities. Large variability is also present, especially at optical/UV and X-ray frequencies. Gamma-ray variability cannot be evaluated as the Fermi data that we are using are averaged over the entire LBAS data taking period. The γ-ray variability of Fermi LBAS blazars is discussed in detail in a separate paper (Abdo et al. 2010b).
A complete description of the γ-ray spectral shape of LBAS sources is given in Abdo et al (2010a). Here we note that in most cases the Fermi data cannot be fit by a simple power law as significant curvature is detected. Downward (convex) curvature is often observed in sources where synchrotron peak is located at low energies (e.g., PKS0454-234, PKS1454-354 and PKS1502+106, 3C454.3 etc.) whereas very flat or even concave type curvature is exhibited by high synchrotron peaked objects (e.g., 3C66A, PKS 0447-439, 1ES 0502+675, and PG 1246+586). A possible explanation of these features is discussed in Section 7.
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Source Name | Period of Observations | Instrument | Reference |
---|---|---|---|
0FGL | |||
(1) | (2) | (3) | (4) |
J0222.6+4302 | 2007–2008 | VERITAS | Acciari et al. 2009a |
J0722.0+7120 | 2008 Apr 22–24 | MAGIC | Teshima 2008 |
J1104.5+3811 | 2004 Nov–2005 Apr | MAGIC | Albert et al. 2007a |
J1221.7+2814 | 2008 Jan–Apr | VERITAS | Acciari et al. 2009b |
J1256.1 − 0547 | 2006 Jan–Apr | MAGIC | Errando et al. 2008 |
J1653.9+3946 | 2005 May–Jul | MAGIC | Albert et al. 2007b |
J2000.2+6506 | 2004 Sept–Oct | MAGIC | Albert et al. 2006 |
J2158.8 − 3014 | 2002 Jul, Oct, 2003 Jul–Sep | HESS | Aharonian et al. 2009 |
J2202.4+4217 | 2005 Aug–Dec, 2006 Jul–Sep | MAGIC | Albert et al. 2007b |
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5. BLAZAR SED OBSERVATIONAL PARAMETERS
We now estimate some key observational parameters that characterize the SED of our blazars, namely, the radio spectral index (αr), the peak frequency and peak flux of the synchrotron component (νSpeak and νSpeak F(νSpeak)), and the peak frequency and flux of the inverse Compton part of the SED (νICpeak and νICpeak F(νICpeak)).
5.1. The Radio Spectral Slope
To estimate the blazar spectral slope (αr, where ) in the radio/mm band we performed a linear regression of all the radio flux measurements that have been used for the SED, including the non-simultaneous ones. The set of frequencies used for the linear regression is not the same for every source but ranged from below 1 GHz up to about 100 GHz, for those sources for which microwave flux measurements are available. The distribution of the radio spectral slopes αr obtained with this method has an average value 〈αr〉 = −0.03 and a standard deviation σ = 0.23 (see Figure 25). Figure 26 shows the distribution of the radio spectral slopes between ∼1 GHz and 8.4 GHz taken from the CRATES catalog (Healey et al. 2007) for the subsample of FSRQs and BL Lac objects, respectively. The distributions shown in Figures 25 and 26 are all very similar with an almost identical average value 〈αr〉 ∼ 0.0 and similar standard deviations σ∼ 0.2/0.3. In particular, for the αr distributions of FSRQs and BL Lacs shown in Figure 26 a Kolmogorov–Smirnov test gives a probability of 0.43 that they come from the same parent population. We conclude that the radio to microwave spectral slope in our SED is quite flat (〈αr〉 ∼ 0) and consistent with being the same in all blazar types.
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Standard image High-resolution image5.2. The αox–αro Plane
The αox–αro plot of the LBAS sample is shown in Figure 27 which also includes all blazars in the BZCat catalog for which we have radio, optical, and X-ray measurements (small red dots). Note that Fermi FSRQs (filled circles), like all FSRQs discovered in any other energy band, are exclusively located along the top-left/bottom-right band, whereas BL Lacs (open circles) can be found in all parts of the plane, albeit with a prevalence in the horizontal area defined by values of αro between 0.2 and 0.4, which is where HBL sources are located (Padovani & Giommi 1995). The area of the αox–αro space where the hypothetical population of ultra high energy peaked (UHBLs) blazars (that is, sources where the synchrotron component is so energetic as to peak in the MeV region; Ghisellini 1999; Giommi et al. 2001) could have been found, is empty, implying that these sources are either very rare, very weak, or non-existent (see also Costamante et al. 2007).
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Standard image High-resolution image5.3. The Synchrotron Peak Energy (νSpeak) and Peak Intensity (νSpeak F(νSpeak))
We estimated the peak energy (νSpeak) and peak intensity (νSpeak F(νSpeak)) of the synchrotron power from the SED reported in Figures 1–24 by fitting the part of the SED that is dominated by synchrotron emission. As a fitting function we used a simple third-degree polynomial (see Kubo et al. 1998):
In the case of high redshift sources (e.g., J0229.5 − 3640, J0921.0+4437 and J1457.4 − 3538, J1522.2+3143), we excluded from the fitting procedure all points in the optical/UV bands that are likely to be significantly affected by Lyα forest absorption.
5.4. An Empirical Method to Derive νSpeak and νSpeak F(νSpeak) from αox and αro
As shown by Padovani & Giommi (1995) the peak of the synchrotron power νSpeak in the SED of a blazar determines its position in the αox–αro plane (see Figure 12 of Padovani & Giommi (1995), see also Padovani et al. (2003)). Here we exploit this dependence showing that the value of νSpeak can be estimated from αox–αro through the following analytical relationship,
where X = 0.565 −1.433· αro + 0.155 · αox and Y = 1.0 −0.661· αro −0.339· αox
We have calibrated this relationship using the νSpeak values directly measured from our 48 quasi-simultaneous SED and the corresponding αox and αro values.
Figure 28 (top panel) shows the values of log(νSpeak) estimated from Equation (3) plotted against the values of log(νSpeak) measured by fitting a SSC model to the synchrotron part of the quasi-simultaneous SED of Figures 1 to 24. The distribution of the difference between the values estimated with the two methods has a mean value of 0.04 and a standard deviation of 0.58, implying that the value of log(νSpeak) can be derived even from non-simultaneous values of αox and αro within 0.6 decade at 1σ level and within one decade in almost all cases.
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Standard image High-resolution imageIt must be noted, however, that this method assumes that the optical and X-ray fluxes are not contaminated by thermal emission from the disk or accretion. In blazars where thermal flux components are not negligible (this should probably occur more frequently in low radio luminosity sources) the method described above may lead to a significant overestimation of the position of νSpeak.
The peak flux νSpeak F(νSpeak) can be estimated using the following relationship:
where R5 GHz is the radio flux density at 5 GHz in units of mJy.
Figure 28 (bottom panel) plots the value of νSpeak F(νSpeak) estimated with the two methods. Also in this case the match is very good with an average value of −0.01 for the difference between the two estimates and a standard deviation of 0.33.
It is quite remarkable that one can derive the synchrotron peak flux simply from νSpeak and from the radio flux as this implies that within a factor of 10 the radio emission represents a long-term calorimeter for the whole jet activity and the basic source power.
5.5. The Peak Frequency and Peak Intensity of the Inverse Compton Bump
We have estimated the peak of the inverse Compton power in the SED (νICpeak) and the corresponding peak flux (νICpeak F(νICpeak)) by fitting the X-ray to γ-ray part of the SED, which is dominated by inverse Compton emission using the polynomial function of Equation (2).
There are some objects in which the soft X-ray band is still dominated by synchrotron radiation, and only the Fermi data can be used to constrain the inverse Compton component, so the above method is subject to large uncertainties. For this reason, in these cases, we have used the ASDC SED97 interface to fit the simultaneous data points to a SSC model with a log-parabolic electron spectrum (Tramacere et al. 2009).
The polynomial fits described above are a very good representation of the data for almost all the SED shown in Figures 1–24; the only two significant exceptions are 3C66A (see Figure 3, left side) and 3C273 (see Figure 15, right side). In the first case, this could be the result of the short-term variability that is clearly visible in the optical/UV and X-ray data. While the γ-ray photons were collected during the Fermi data taking period the synchrotron, and inverse Compton, peak frequencies probably changed causing the unusual shape of the spectrum which reflects the average of all the physical states the source went through during the long γ-ray observation. In the case of 3C273 the excess of optical/UV light above the polynomial fit is attributed to the source strong blue continuum which is due to accretion and not non-thermal radiation; for this reason, this part of the spectrum was excluded from the fit.
For the whole sample we have determined νICpeak as the value of ν which maximizes νFν in Equation (2) or the predictions of the SSC model. The results are reported in Columns 6 and 7 of Table 13. The best fit to both the synchrotron and inverse Compton components appears as dashed lines in Figures 1–24.
Table 13. Blazar SED Parameters
Name | SED | αr | log(νSpeak) | log(νSpeak F(νSpeak)) | log(νICpeak) | log(νICpeak F(νICpeak)) | log(γSSCpeak) | Compton | SED | Optical |
---|---|---|---|---|---|---|---|---|---|---|
0FGL | Available | Dominance | Classification | Classification | ||||||
(1) | (2) | (3)a | (4)b | (5)b | (6)c | (7) | (8)d | (9) | (10) | (11) |
J0017.4 − 0503 | ... | 0.127 | −/13.6 | −/−11.4 | −/20.7 | ... | 3.4 | ... | LSP | FSRQ |
J0033.6 − 1921 | Yes | 0 | 16.1/16.3 | −11.1/−11.2 | 24.3/24.8 | −11.1 | 4 | 1 | HSP | BL Lac |
J0050.5 − 0928 | Yes | 0.205 | 14.3/14.4 | −10.8/−10.6 | 22.4/23 | −10.6 | 4 | 1.8 | ISP | BL Lac |
J0051.1 − 0647 | ... | −0.103 | −/12.8 | −/−11.4 | −/22.7 | ... | 4.9 | ... | LSP | FSRQ |
J0100.2+0750 | ... | −0.076 | −/− | −/− | −/24.4 | ... | ... | ... | ... | Unidentified |
J0112.1+2247 | ... | 0.121 | −/14.6 | −/−10.8 | −/23.1 | ... | 4.1 | ... | ISP | BL Lac |
J0118.7 − 2139 | ... | 0.089 | −/13 | −/−11.5 | −/22.3 | ... | 4.5 | ... | LSP | FSRQ |
J0120.5 − 2703 | ... | −0.114 | −/13.9 | −/−10.8 | −/23.6 | ... | 4.7 | ... | LSP | BL Lac |
J0136.6+3903 | ... | 0 | −/16 | −/−10.9 | −/24.9 | ... | 4.4 | ... | HSP | BL Lac |
J0137.1+4751 | Yes | 0.192 | 13.6/13.3 | −10.5/−10.8 | 22.6/22.8 | −10.6 | 4.4 | 0.8 | LSP | FSRQ |
J0144.5+2709 | ... | 0.011 | −/− | −/− | −/22.7 | ... | ... | ... | ... | BL Lac |
J0145.1 − 2728 | ... | −0.199 | −/13.3 | −/−11.2 | −/21.4 | ... | 3.9 | ... | LSP | FSRQ |
J0204.8 − 1704 | ... | −0.017 | −/13.3 | −/−11 | −/21.6 | ... | 4.1 | ... | LSP | FSRQ |
J0210.8 − 5100 | Yes | −0.099 | 12.5/13.8 | −10.7/−10.4 | 22.4/22.4 | −10.2 | 4.8 | 3.6 | LSP | FSRQ |
J0217.8+0146 | ... | 0.237 | −/12.9 | −/−11.1 | −/23 | ... | 5 | ... | LSP | FSRQ |
J0220.9+3607 | ... | −0.186 | −/12.4 | −/−11.4 | −/21.1 | ... | 4.3 | ... | LSP | FSRQ |
J0222.6+4302 | Yes | 0 | 15.1/14.4 | −10.2/−10.6 | 24.2/23.7 | −10.2 | 4.4 | 1 | ISP | BL Lac |
J0229.5 − 3640 | Yes | 0 | 13.5/13 | −11.7/−12 | 21.8/21.3 | −10.4 | 4.1 | 20.3 | LSP | FSRQ |
J0238.4+2855 | Yes | 0.126 | 12.8/12.8 | −10.7/−11 | 22.1/21.6 | −10.8 | 4.6 | 0.9 | LSP | FSRQ |
J0238.6+1636 | Yes | 0.557 | 13.5/13.1 | −10/−10.9 | 23.2/23.3 | −9.9 | 4.8 | 1.5 | LSP | BL Lac |
J0245.6 − 4656 | ... | −0.397 | −/13.1 | −/−11.2 | −/22.2 | ... | 4.4 | ... | LSP | BZU |
J0303.7 − 2410 | ... | −0.664 | −/15.1 | −/−10.6 | −/23.5 | ... | 4.1 | ... | HSP | BL Lac |
J0334.1 − 4006 | ... | −0.036 | −/13.3 | −/−11 | −/23 | ... | 4.8 | ... | LSP | BL Lac |
J0349.8 − 2102 | Yes | 0.014 | 12.9/13 | −11.3/−11.6 | 21.8/21.3 | −10.2 | 4.4 | 13.5 | LSP | FSRQ |
J0407.6 − 3829 | ... | 0 | −/13.6 | −/−11 | −/22.3 | ... | 4.2 | ... | LSP | Unidentified |
J0412.9 − 5341 | ... | −0.513 | −/− | −/− | −/22.4 | ... | ... | ... | ... | Unidentified |
J0423.1 − 0112 | Yes | −0.081 | 13.4/13.3 | −10.9/−10.5 | 21.7/22 | −10.3 | 4 | 4.1 | LSP | FSRQ |
J0428.7 − 3755 | Yes | 0.419 | 13.3/13.6 | −11/−10.8 | 22.8/23 | −10.2 | 4.6 | 6.3 | LSP | BL Lac |
J0449.7 − 4348 | Yes | −0.498 | 15.6/15.4 | −10.2/−10.6 | 23.9/23.5 | −10.5 | 4.1 | 0.5 | HSP | BL Lac |
J0457.1 − 2325 | Yes | −0.074 | 13.1/13 | −11/−11 | 22.8/22.6 | −9.9 | 4.7 | 12.5 | LSP | FSRQ |
J0507.9+6739 | Yes | 0 | 16.6/16.3 | −10.7/−11 | 24.3/24.9 | −10.5 | 3.7 | 1.4 | HSP | BL Lac |
J0516.2 − 6200 | Yes | 0.226 | 13.6/13 | −11.3/−11.5 | 22.5/22.9 | −10.7 | 4.4 | 4.1 | LSP | BZU |
J0531.0+1331 | Yes | 0.239 | 12.8/13.1 | −10.9/−10.7 | 21.3/21.4 | −9.8 | 4.2 | 11.6 | LSP | FSRQ |
J0538.8 − 4403 | Yes | −0.084 | 13.4/13.6 | −10.6/−10.3 | 22.7/22.8 | −10.1 | 4.6 | 3.6 | LSP | BL Lac |
J0654.3+5042 | ... | 0.231 | −/− | −/− | −/23.5 | ... | ... | ... | ... | BZU |
J0654.3+4513 | ... | 0.005 | −/13 | −/−11.6 | −/22.3 | ... | 4.6 | ... | LSP | FSRQ |
J0700.0 − 6611 | ... | −0.173 | −/14.1 | −/−11.2 | −/23.6 | ... | 4.6 | ... | ISP | BZU |
J0712.9+5034 | Yes | 0.403 | 13.6/14.3 | −11.3/−11.4 | 23/23.4 | −11 | 4.6 | 2.1 | ISP | BL Lac |
J0714.2+1934 | ... | 0 | −/− | −/− | −/22.1 | ... | ... | ... | ... | BZU |
J0719.4+3302 | ... | −0.149 | −/13.6 | −/−11.4 | −/22.1 | ... | 4.2 | ... | LSP | FSRQ |
J0722.0+7120 | Yes | −0.126 | 14.6/14.4 | −9.9/−10.6 | 23.3/23.2 | −10.4 | 4.2 | 0.3 | ISP | BL Lac |
J0730.4 − 1142 | Yes | 0 | 13.1/12.8 | −11.1/−10.7 | 22.6/22.5 | −10 | 4.6 | 10.1 | LSP | FSRQ |
J0738.2+1738 | ... | 0.271 | −/13.8 | −/−10.6 | −/23.1 | ... | 4.6 | ... | LSP | BL Lac |
J0818.3+4222 | ... | −0.042 | −/12.6 | −/−11.2 | −/23.3 | ... | 5.2 | ... | LSP | BL Lac |
J0824.9+5551 | ... | 0.095 | −/13 | −/−11.2 | −/20.3 | ... | 3.5 | ... | LSP | FSRQ |
J0855.4+2009 | Yes | 0.443 | 13.4/13.9 | −9.8/−10.4 | 21.4/22.3 | −10.5 | 3.9 | 0.2 | LSP | BL Lac |
J0909.7+0145 | ... | 0.193 | −/− | −/− | −/20.9 | ... | ... | ... | ... | BL Lac |
J0921.2+4437 | Yes | 0.153 | 13.4/12.6 | −11.2/−11.4 | 22/22.2 | −10.6 | 4.2 | 3.3 | LSP | FSRQ |
J0948.3+0019 | ... | 0.645 | −/13.8 | −/−11.3 | −/21.1 | ... | 3.6 | ... | LSP | FSRQ |
J0957.6+5522 | ... | −0.41 | −/13.1 | −/−10.9 | −/23.5 | ... | 5 | ... | LSP | FSRQ |
J1012.9+2435 | ... | −0.19 | −/14.8 | −/−11.3 | −/22.7 | ... | 3.9 | ... | ISP | FSRQ |
J1015.2+4927 | Yes | −0.239 | 16.3/15.5 | −10.5/−10.5 | 24.5/24.6 | −10.6 | 3.9 | 0.8 | HSP | BL Lac |
J1015.9+0515 | ... | −0.178 | −/− | −/− | −/22.7 | ... | ... | ... | ... | FSRQ |
J1034.0+6051 | ... | −0.054 | −/12.8 | −/−11.6 | −/21.6 | ... | 4.3 | ... | LSP | FSRQ |
J1053.7+4926 | ... | 0 | −/15 | −/−11.3 | −/25.9 | ... | 5.3 | ... | ISP | BL Lac |
J1054.5+2212 | ... | 0 | −/14.6 | −/−11.6 | −/22.6 | ... | 3.9 | ... | ISP | BL Lac |
J1058.9+5629 | Yes | −0.115 | 14.6/15 | −10.9/−10.8 | 22.3/23.1 | −11 | 3.7 | 0.7 | ISP | BL Lac |
J1057.8+0138 | Yes | 0.002 | 13.1/13.1 | −10.8/−10.7 | 22/22.7 | −10.8 | 4.3 | 1 | LSP | BZU |
J1100.2 − 8000 | ... | 0.489 | −/13.4 | −/−10.8 | −/20.7 | ... | 3.6 | ... | LSP | BL Lac |
J1104.5+3811 | Yes | −0.109 | 16.6/16.1 | −9.4/−9.8 | 25/24.5 | −9.9 | 4.1 | 0.3 | HSP | BL Lac |
J1129.8 − 1443 | ... | −0.387 | −/13.3 | −/−10.6 | −/20.8 | ... | 3.7 | ... | LSP | FSRQ |
J1146.7 − 3808 | ... | 0.217 | −/13.6 | −/−10.6 | −/22.7 | ... | 4.4 | ... | LSP | FSRQ |
J1159.2+2912 | Yes | −0.286 | 13.1/13.5 | −10.7/−10.9 | 22/21.6 | −10.5 | 4.3 | 1.8 | LSP | FSRQ |
J1218.0+3006 | ... | −0.299 | −/15.5 | −/−10.3 | −/24 | ... | 4.1 | ... | HSP | BL Lac |
J1221.7+2814 | Yes | 0.194 | 14.5/14.1 | −10.6/−10.6 | 24/23.8 | −10.6 | 4.7 | 0.8 | ISP | BL Lac |
J1229.1+0202 | Yes | −0.158 | 13.5/13 | −9.8/−9.7 | 21/20.7 | −9.6 | 3.6 | 1.3 | LSP | FSRQ |
J1246.6 − 2544 | ... | 0.245 | −/13.4 | −/−10.7 | −/22.6 | ... | 4.5 | ... | LSP | FSRQ |
J1248.7+5811 | Yes | 0.147 | 14.6/15 | −11/−10.7 | 22.1/23.8 | −10.9 | 3.7 | 1.2 | ISP | BL Lac |
J1253.4+5300 | ... | −0.165 | −/13.9 | −/−11.2 | −/22.9 | ... | 4.4 | ... | LSP | BL Lac |
J1256.1 − 0548 | Yes | 0.541 | 12.6/13.1 | −10.3/−10.2 | 22.2/22.1 | −10.3 | 4.7 | 1.1 | LSP | FSRQ |
J1310.6+3220 | Yes | 0.304 | 13.1/12.5 | −10.9/−11.4 | 22.5/22.6 | −10.4 | 4.6 | 3.3 | LSP | FSRQ |
J1331.7 − 0506 | ... | 0.083 | −/13.1 | −/−11.4 | −/21.2 | ... | 3.9 | ... | LSP | FSRQ |
J1333.3+5058 | ... | 0 | −/− | −/− | −/22 | ... | ... | ... | ... | FSRQ |
J1355.0 − 1044 | ... | −0.37 | −/13.6 | −/−11.1 | −/22.1 | ... | 4.1 | ... | LSP | FSRQ |
J1427.1+2347 | ... | −0.338 | −/14.9 | −/−10.7 | −/24.3 | ... | 4.6 | ... | ISP | BL Lac |
J1457.6 − 3538 | Yes | −0.054 | 13.6/13 | −10.9/−11.5 | 22.7/22.6 | −10.2 | 4.4 | 5.6 | LSP | FSRQ |
J1504.4+1030 | Yes | −0.03 | 13.6/12.5 | −11/−11.1 | 22.9/22.9 | −9.8 | 4.6 | 16.6 | LSP | FSRQ |
J1511.2 − 0536 | ... | 0 | −/13.3 | −/−10.9 | −/21.9 | ... | 4.2 | ... | LSP | FSRQ |
J1512.7 − 0905 | Yes | 0 | 13.1/13.6 | −10.6/−10.6 | 22.3/21.6 | −9.7 | 4.5 | 7.4 | LSP | FSRQ |
J1517.9 − 2423 | ... | 0.085 | −/13.8 | −/−10.6 | −/23.8 | ... | 4.9 | ... | LSP | BL Lac |
J1522.2+3143 | Yes | 0.182 | 13.3/12.9 | −11.5/−11.8 | 22.4/22 | −10.2 | 4.5 | 23.3 | LSP | FSRQ |
J1543.1+6130 | Yes | 0.268 | 14.1/14.6 | −11.2/−11.3 | 23.5/23.5 | −11.1 | 4.6 | 1.1 | ISP | BL Lac |
J1553.4+1255 | ... | −0.474 | −/− | −/− | −/22.6 | ... | ... | ... | ... | FSRQ |
J1555.8+1110 | ... | 0.258 | −/15.4 | −/−10.3 | −/24.7 | ... | 4.6 | ... | HSP | BL Lac |
J1625.8 − 2527 | ... | −0.04 | −/12.4 | −/−11.1 | −/22 | ... | 4.7 | ... | LSP | FSRQ |
J1625.9 − 2423 | ... | 0.162 | −/− | −/− | −/21.7 | ... | ... | ... | ... | Unidentified |
J1635.2+3809 | ... | −0.085 | −/13.1 | −/−10.7 | −/21.8 | ... | 4.2 | ... | LSP | FSRQ |
J1641.4+3939 | ... | 0.282 | −/12.9 | −/−11.2 | −/21.8 | ... | 4.4 | ... | LSP | FSRQ |
J1653.9+3946 | Yes | −0.189 | 17.1/15.3 | −10.3/−10 | 24.7/24.7 | −10.5 | 3.7 | 0.5 | HSP | BL Lac |
J1719.3+1746 | Yes | 0.032 | 13.5/13.6 | −11.3/−11.2 | 24.7/24.2 | −10.7 | 5.5 | 4.6 | LSP | BL Lac |
J1751.5+0935 | Yes | 0.64 | 13.1/13.5 | −10.8/−10.6 | 22.2/22.5 | −10.3 | 4.4 | 3 | LSP | BL Lac |
J1802.2+7827 | ... | 0.129 | −/13.8 | −/−10.5 | −/22.5 | ... | 4.3 | ... | LSP | BL Lac |
J1847.8+3223 | ... | 0.106 | −/13.1 | −/−11.3 | −/22.1 | ... | 4.4 | ... | LSP | FSRQ |
J1849.4+6706 | Yes | −0.063 | 13.5/13.5 | −10.6/−11.1 | 22.5/22.9 | −10.5 | 4.4 | 1.3 | LSP | FSRQ |
J1911.2 − 2011 | ... | 0.055 | −/12.6 | −/−11.1 | −/21.8 | ... | 4.5 | ... | LSP | FSRQ |
J1923.3 − 2101 | ... | −0.092 | −/13.3 | −/−10.7 | −/22.3 | ... | 4.4 | ... | LSP | FSRQ |
J2000.2+6506 | Yes | −0.083 | 16.6/15.9 | −10/−10.3 | 24.7/24.1 | −10.5 | 3.9 | 0.3 | HSP | BL Lac |
J2009.4 − 4850 | ... | −0.182 | −/15.3 | −/−10 | −/24.1 | ... | 4.3 | ... | HSP | BL Lac |
J2017.2+0602 | ... | 0 | −/14.3 | −/−11.9 | −/24.1 | ... | 4.8 | ... | ISP | Unidentified |
J2025.6 − 0736 | ... | −0.339 | −/12.9 | −/−11.4 | −/22.3 | ... | 4.6 | ... | LSP | FSRQ |
J2056.1 − 4715 | ... | −0.161 | −/12.9 | −/−11 | −/21.3 | ... | 4.1 | ... | LSP | FSRQ |
J2139.4 − 4238 | ... | 0.093 | −/14.8 | −/−11.2 | −/23.5 | ... | 4.3 | ... | ISP | BL Lac |
J2143.2+1741 | Yes | 0.48 | 14.1/13.9 | −10.4/−10.8 | 22/21.3 | −10.5 | 3.8 | 0.8 | LSP | FSRQ |
J2147.1+0931 | ... | 0.027 | −/13.5 | −/−10.9 | −/21.4 | ... | 3.9 | ... | LSP | FSRQ |
J2157.5+3125 | ... | 0.07 | −/12.9 | −/−11.6 | −/21.9 | ... | 4.4 | ... | LSP | FSRQ |
J2158.8 − 3014 | Yes | −0.179 | 16/16.5 | −9.7/−9.8 | 23.9/24.1 | −10.2 | 3.9 | 0.3 | HSP | BL Lac |
J2202.4+4217 | Yes | 0 | 13.6/13.8 | −10.1/−10.4 | 21.9/22.6 | −10.8 | 4 | 0.2 | LSP | BL Lac |
J2203.2+1731 | ... | 0.317 | −/12.9 | −/−11.4 | −/22.5 | ... | 4.7 | ... | LSP | FSRQ |
J2207.0 − 5347 | ... | −0.12 | −/13 | −/−11.1 | −/21 | ... | 3.9 | ... | LSP | FSRQ |
J2229.8 − 0829 | ... | 0.127 | −/13.4 | −/−10.7 | −/20.9 | ... | 3.6 | ... | LSP | FSRQ |
J2232.4+1141 | ... | 0 | −/13.1 | −/−10.7 | −/21.1 | ... | 3.9 | ... | LSP | FSRQ |
J2254.0+1609 | Yes | −0.112 | 13.6/13.8 | −9.5/−9.8 | 22.5/21.9 | −9.3 | 4.3 | 1.7 | LSP | FSRQ |
J2325.3+3959 | ... | −0.003 | −/14 | −/−11.6 | −/24 | ... | 4.9 | ... | LSP | BL Lac |
J2327.3+0947 | Yes | −0.08 | 13.1/13 | −11/−11.4 | 21.5/20.6 | −10.3 | 4.1 | 5.1 | LSP | FSRQ |
J2345.5 − 1559 | Yes | 0.385 | 13.3/13.3 | −11.7/−11.3 | 22.5/21.9 | −10.7 | 4.5 | 9.7 | LSP | FSRQ |
Notes. aThe radio power-law spectral index αr is evaluated in the range 1–100 GHz. bThe value to the left is estimated directly from SED, while the value reported to the right has been estimated from αox–αro. cThe value to the left is estimated directly from SED, while the value reported to the right has been estimated from Equation (5). dCalculated assuming a simple SSC emission mechanism, i.e., γSSCpeak = .
Figure 29 (bottom panel) shows that the νICpeak, derived as described above for the 48 sources for which we have built the SED, is strongly correlated with their γ-ray spectral slope (Γ) taken from Table 3 of Abdo et al. (2009b). We note that the scatter in the plots of Figure 29 is largest in the regions of low νSpeak/νICpeak–steep values of Γ, probably reflecting the presence of γ-ray spectral curvature (see Section 4). The best fit to the νICpeak–Γ relationship is
Since the 48 objects for which we have quasi-simultaneous SED are representative of the entire LBAS sample, the above equation can be used to estimate the νICpeak of the LBAS sources for which we have no simultaneous SED. We have done so and we have listed the results in Column 6 of Table 13. The statistical uncertainty associated with νICpeak calculated via Equation (5) can be estimated from the distribution of the difference between νICpeak measured from the SED and that from Equation (5). This distribution is centered on the value of 0 and has a sigma of 0.51; considering that the value of νICpeak from the SED is also subject to a similar error we conservatively conclude that the log of νICpeak values estimated through Equation (5) has an associated error of about 0.7.
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Standard image High-resolution image6. AN SED-BASED CLASSIFICATION SCHEME FOR BLAZARS AND OTHER AGNs
Blazars, like other types of AGNs, have been classified in the past according to heterogeneous criteria, often based on observational properties related to the energy band where they were first discovered. This lack of a stable and clear definition can lead to multiple classification of the same object and may cause subtle selection effects and biases in statistical analyses. Now that Fermi has started producing large and homogeneous samples of blazars it is useful to re-assess the issue of blazar classification from a physical viewpoint taking into account the results of our SED study, so as to build a more robust base for future statistical/populations work.
We describe here a physical classification scheme based on the widely accepted AGN standard paradigm (e.g., Urry & Padovani 1995) and on well-known radiation emission processes.
The radiation emitted by an AGN is usually attributed to one (or both) of the following two physical processes.
- 1.Thermal radiation originating from in-falling matter strongly heated in the inner parts of an accretion disk close to the black hole. This radiation is often assumed to be Comptonized by a hot corona producing the power-law X-ray emission.
- 2.Non-thermal emission emitted in a magnetic field by highly energetic particles that have been accelerated in a jet of material ejected from the nucleus at relativistic speed.
The first process produces radiation mostly in the optical, UV, and X-ray bands, whereas the radiation produced through the second mechanism encompasses the entire electromagnetic spectrum, from radio waves, to the most energetic γ-rays. AGNs that are energetically dominated by thermal radiation (in the optical-X-ray band) can be classified as thermal-dominated, or disk-dominated AGNs, whereas AGNs where the non-thermal processes are energetically dominant at all frequencies can be classified as non-thermal radiation dominated or jet-dominated AGNs. AGNs can therefore be subdivided as follows.
- 1.Thermal/disk-dominated AGNsThese are objects usually called QSOs or Seyfert galaxies which do not show significant nuclear radio emission compared to the observed emission in the optical or X-ray band. Although thermal-dominated AGNs are the large majority (≈90 %) of AGNs, here we do not go into further detail about their sub-classification since none of the sources so far detected by Fermi is thermal/disk dominated.We feel, however, that it is necessary to consider this type of AGN in this context as in some cases both the accretion (thermal) and the jet (non-thermal) component may be present in the optical, UV, or X-ray flux of the same object (e.g., 3C120, 3C 273; Grandi et al. 2004). This mix of accretion and non-thermal radiation is rarely seen in the very bright γ-ray sources detected so far, but it will probably become more common as the sensitivity of the Fermi survey increases with time and a large number of fainter and less aligned sources are detected.
- 2.Non-thermal/jet-dominated AGNsThe class of non-thermal/jet powered AGNs corresponds to the usual type of sources known as radio loud AGNs. These can be subdivided into blazars and non-aligned non-thermal dominated AGNs depending on the orientation of their jets with respect to the line of sight.
- (a)Blazars. These are core-dominated flat or inverted radio spectrum radio loud AGNs. The radio core dominance and the flat radio spectrum together with strong and rapid variability (including superluminal motion) are the observational indicators that these objects point their radio jet in a direction that is closely aligned to our line of sight. Because of this very special perspective their light is strongly amplified by relativistic effects and the time-scales of observed variations are significantly shortened.Blazars are divided into two main subclasses, FSRQs and BL Lacs, depending on their optical spectral properties:
- (i)FSRQs or Blazars of the QSO type or BZQ (Massaro et al. 2009). These are blazars showing broad emission lines in their optical spectrum just like normal QSOs. This category includes objects normally referred to as FSRQs and broad-line radio galaxies.
- (ii)BL Lacs or Blazars of the BL Lac type or BZB (Massaro et al. 2009) These are objects normally called BL Lacs or BL Lacertae objects. Their radio compactness and broadband SED are very similar to that of strong lined blazars but they have no strong and broad lines in their optical spectrum (see e.g., Marchã et al. 1996).Sometimes, objects which show many of the hallmarks of blazars do not have optical spectra of sufficient quality to safely determine the presence of broad emission lines or to accurately measure their equivalent width. In these cases, the blazar subclass cannot be established and therefore these objects have to be referred to as BZU or Blazars of the Unknown type (see also Massaro et al. 2009).
- (b)Non-aligned non-thermal dominated AGNs. These sources are radio loud AGNs with jets pointed at large or intermediate (≈15°–40°, see Urry & Padovani 1995) angles with respect to the line of sight. For this reason they are sometimes called non-aligned, misaligned, or mispointed blazars. This category includes:
- (i)Radio galaxies or non-aligned non-thermal dominated AGNs with no broad emission lines which are sources often showing extended, double-sided radio jets/lobes pointing in opposite directions in the plane of the sky with respect to the central nucleus. The jet is clearly oriented at a very large angle with respect to the line of sight. The nuclear emission is similar to that of blazars but it is not amplified and therefore it is usually fainter than the extended emission, especially at low radio frequencies. The broad emission lines are not present in these sources because at such large angles they are hidden by the torus.
- (ii)SSRQ or non-aligned non-thermal dominated AGNs with broad emission lines which are sources usually known as steep spectrum radio quasars (SSRQ); hence, the orientation of the jet in these sources is thought to be intermediate between that of blazars and radio galaxies Urry & Padovani 1995).
In the literature, BL Lac objects are often subdivided into two or three subclasses depending on their SED. This classification was first introduced by Padovani & Giommi (1995) who used the peak energy of the synchrotron emission, which reflects the maximum energy the particles can be accelerated in the jet, to classify BL Lac into low-energy and high-energy synchrotron peak objects, respectively called LBL and HBL. In the following, we extend this definition to all types of non-thermal dominated AGNs using new acronyms (LSP, ISP, and HSP) to avoid confusion.
- 1.LSP or low synchrotron peaked blazars. These are sources where the synchrotron power peaks at low energy (i.e., in the far-IR or IR band or νpeak ≲ 1014 Hz) and therefore their X-ray emission is flat (αx ≈ 0.4–0.7) and due to the rising part of the inverse Compton component (see Figure 30). At these relatively low energies the inverse Compton scattering occurs in the Thomson regime (see Section 7 and Figure 34).
- 2.ISP or intermediate synchrotron peaked blazars. Sources where the synchrotron emission peaks at intermediate energies (1014 ≲ νpeak ≲ 1015 Hz). In this case, the X-ray band includes both the tail of the synchrotron emission and the rise of the inverse Compton component (see Figure 30).
- 3.HSP or high synchrotron peaked blazars. Sources where the emitting particles are accelerated at much higher energies than in LSPs so that the peak of the synchrotron power reaches UV or higher energies (νpeak ≳ 1015 Hz) (see Figure 30; Padovani & Giommi 1996). Under these conditions the synchrotron emission dominates the observed flux in the X-ray band and the inverse Compton scattering occurs in the Klein Nishina regime (see Section 7 and Figure 34).
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Standard image High-resolution imageIdeally, blazars should be classified on the basis of a complete SED built with simultaneous data. As in most cases this is not possible, LSP or HSP objects can still be recognized by estimating their νSpeak from αox and αro and from their X-ray spectral shape or by their radio to X-ray spectral slope (Padovani et al. 2003).
In LSP sources the X-ray spectrum is flat (photon spectral index 1.5 <γx < 1.8) and dominated by the IC component. In HSP sources, the X-ray spectrum is instead still due to synchrotron emission and it is usually steep (γx > 2) if νSpeak ≲1017 Hz, but it can still be flat in extreme HSPs where νSpeak is well into the X-ray band; the radio to X-ray spectral index, αrx, of these blazars is less than 0.7. In ISP objects both the (steep) tail of the synchrotron emission and the (flat) rise of the IC component are within the X-ray band (see Figure 30), and 0.7 ≲ αrx ≲ 0.8.
6.1. The Distribution of Synchrotron and Inverse Compton Peak Frequencies
Now that we have a new SED-based classification of blazars and we have a reliable method of estimating νSpeak, we inspect the LBAS sample in terms of its content of LSP, ISP, and HSP objects and we compare it with that of samples selected in other energy bands.
The distribution of the synchrotron peak frequency (νSpeak) of LBAS blazars (estimated using the αox–αro method) is plotted in Figure 31 for the FSRQ and the BL Lac subsamples (top and bottom panels respectively, solid histograms). While the νSpeak distribution of FSRQs starts at ∼1012.5 Hz, peaks at ∼1013.3 Hz, and does not extend beyond ≈1014.5 Hz, the distribution of BL Lacs is much flatter, starts at ∼1013 Hz, and reaches much higher frequencies(≈1017 Hz) than that of FSRQs. For comparison, in the same figure, we plot as a dotted histogram the distribution of νSpeak of the sample of FSRQs and BL Lacs detected as foreground sources in the WMAP 3 yr microwave anisotropy maps (Giommi et al. 2009). In Figure 32, we compare the νSpeak distribution of the LBAS sample with that of the X-ray selected sample of blazars detected in the Einstein Extended Medium Sensitivity Survey (EMSS; Gioia et al. 1990).
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Standard image High-resolution imageFrom Figures 31 and 32, we see that the νSpeak distribution of FSRQs is consistent with being the same in the γ-ray, radio/microwave and in the X-ray band. We note that the large majority of FSRQs are of the LSP type while no FSRQs of the HSP type have been found at any frequency. On the contrary, the νSpeak distribution of BL Lac objects is very different in the three energy bands. It is strongly peaked at ∼1013.3 Hz in the microwave band, where HBL sources are very rare, whereas in the X-ray and γ-ray bands HSP sources are more abundant than LSPs.
Figure 33 shows the distribution of the inverse Compton peak frequency, νICpeak, of the FSRQs (dot-dashed histogram) and the BL Lacs (solid histogram) in the LBAS sample. The two distributions are quite different from the BL Lacs exhibiting much higher νICpeak values, reproducing the case of the distribution of synchrotron νSpeak shown in Figure 28. This is most likely due to the same reason that causes the different νSpeak distributions in the two blazar subclasses.
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Standard image High-resolution image6.2. Summary of Observational Findings and Sources Classification
The blazar observational parameters estimated from the quasi-simultaneous SED and from the broadband spectral indices αox, αro for the cases where no simultaneous SED are available are summarized in Table 13 where we also classify our blazars according to the scheme described in Section 6. Column 1 gives the source name; Column 2 indicates if the quasi-simultaneous SED for the source is available; Column 3 gives the radio spectral index αr as estimated in Section 5.1; Columns 4 and 5 give the synchrotron peak frequency (νSpeak) and intensity (νSpeak F(νSpeak)) estimated from the SED and with the αox–αro method, respectively; Column 6 and 7 give the inverse Compton bump peak frequency (νICpeak) and intensity (νICpeak F(νICpeak)) estimated from the SED and from the correlation between νICpeak and the γ-ray spectral slope (see Figure 29), respectively; Column 8 gives the particle peak energy (Lorentz factor) estimated assuming a simple SSC model (γSSCpeak = , see Equation (7) of Section 7); Column 9 gives the Compton dominance (νICpeak F(νICpeak)/νSpeak F(νSpeak)); Columns 10 and 11 give the source classification based on the optical spectrum and on the shape of the SED according to the scheme described above.
7. IMPLICATIONS FOR PHYSICAL MODELING
The quasi-simultaneous SED reported in this paper show the typical two bump shape that is seen in radio or X-ray selected blazars. According to current models the low energy bump is interpreted as synchrotron (S) emission from highly relativistic electrons, and the high energy bump is related to inverse Compton (IC) emission of various underlying radiation fields.
In the case of the synchrotron self-Compton model (SSC; Jones et al. 1974; Ghisellini & Maraschi 1989) the seed photons for the IC process are the synchrotron photons produced by the same population of relativistic electrons.
In the case of the external radiation Compton (ERC) scenario (Sikora et al. 1994; Dermer et al. 2002), the seed photons for the IC process are typically UV photons generated by the accretion disk surrounding the black hole, and reflected toward the jet by the broad line region (BLR) within a typical distance from the accretion disk of the order of 1 pc. If the emission occurs at larger distances, the external radiation is likely to be provided by a dusty torus (Sikora et al. 2002). In this case, the photon field is typically peaked at IR frequencies.
In this section, we follow a phenomenological approach to obtain information about the peak Lorentz factor of the electron distribution (γpeak) most contributing to the synchroton emission and to the inverse Compton process. To test the methods used to estimate γpeak, we employ an accurate numerical model (Tramacere et al. 2009; Tramacere 2007; Massaro et al. 2006; Tramacere & Tosti 2003) that can reproduce both the SSC and ERC models. For the electron distribution we considered a log-parabola of the form with γpeak ranging between 100 and 6 × 105 and with curvature parameter r = 0.4 (Massaro et al. 2004; Tramacere et al. 2007). As input parameters for the benchmark SSC model we use a source size R = 1015 cm, a magnetic field B = 0.1 G, a beaming factor δ = 10, and an electron density N = 1 e−cm−3 (N = ∫n(γ)dγ). In the case of the benchmark ERC model, we use the same set of parameters with the addition of the external photon field produced by the accretion disk and reflected by the BLR toward the emitting region with an efficiency τBLR = 0.1. The accretion disk radiation is modeled by a multitemperature black body, with an innermost disk temperature of 105 K.
7.1. The Synchrotron Peak Frequency
The dependence of the observed peak frequency of the synchrotron emission (νSpeak) on magnetic field intensity (B), electron Lorentz factor (γ), beaming factor (δ) and redshift (z) is given by
where is the synchrotron peak frequency in the emitting region rest frame. A good estimate of γSpeak in terms of the differential electron energy distribution (n(γ) = dN(γ)/dγ) is given by the peak of γ3n(γ), hereafter γ3p (Tramacere et al. 2009; Tramacere et al. 2007). In panel (a) of Figure 34, we plot the ratio of γSpeak to γ3p as a function of γSpeak. The ratio is steady and very close to one over the whole range of γSpeak values. The value of γSpeak is estimated by fitting the peak of the numerically computed synchrotron SED with a log-parabolic analytical function. Note, however, that there is a degeneracy on the value of γSpeak given by the product Bδ. We discuss this point in the next subsection.
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Standard image High-resolution image7.2. The Inverse Compton Peak Frequency
In a simple SSC model, and under the Thomson regime (TH) of the IC scattering, the observed peak frequency of the synchrotron component (νSpeak) is related to the observed peak frequency of the inverse Compton one (νICpeak) by the following relation:
where γSSCpeak is of the same order of γSpeak. Panels (b) and (c) of Figure 34 show that (for the choice of SSC parameters reported above) this trend is valid only for γSSCpeak ≲ 2 × 104 where the transition from Thomson to Klein Nishina (KN) regime occurs. In the KN regime, Equation (7) is no longer valid: in fact, the kinematic limit for the maximum energy of the up-scattered photons in the emitting region rest frame is
As the energy of the seed photons in the electron rest frames increases, the maximum up-scattered photon energy approaches the energy of the up-scattering electron (γmec2). This means that the peak energy of the IC emission is no longer growing with γ2peak according to Equation (7), but it starts becoming smaller as shown in panels (b) and (c) of Figure 34. We note that this effect is particularly relevant for the case of HBL objects.
Other deviations from the trend given by Equation (7) occur when further radiative components add to a single zone SSC. In fact, for the case of the external Compton scenario, the observed peak frequency of the ERC component in terms of the frequency of the external photon field in the disk rest frame reads
where is the external photon field frequency transformed to the rest frame of the emitting region which is moving with a bulk Lorentz factor Γ, and assuming that the BLR radiation is isotropic.
If one uses Equation (7) in place of Equation (9) (an assumption justified by the fact that the UV and IR external radiation fields are usually dominated by the non-thermal synchrotron emission of the source), a significant bias on the value of γERCpeak is introduced in the ERC scenario. In fact, the resulting value of γpeak is strongly overestimated in the case of external UV radiation field (γSSCpeak ≫ γERCpeak and γSSCpeak ≫ γSpeak). In the case of the IR external radiation field, the bias is smaller but the measured value of γSSCpeak is still overestimating both γERCpeak and γSpeak.
In conclusion, when γpeak is estimated through Equation (7) we expect two main biases:
- 1.a bias related to the KN effect, affecting mostly HBL objects, which leads to an underestimation of γpeak;
- 2.a bias related to the ERC scenario, affecting FSRQs and IBL objects, which yields an overestimate of γpeak.
These arguments provide an interesting diagnostic tool in the νSpeak–γSSCpeak plane. Objects radiating mainly via the ERC mechanism are expected to lie above the νSpeak ∝ γSpeak line, and objects radiating γ-rays mainly via the SSC mechanism are expected to lie along the νSpeak ∝ γSpeak line in the case of the TH-IC regime, and below it in the case of KN-IC regime.
To test this scenario, we use the value of γSSCpeak obtained by Equation (7) applied to the numerically computed SSC/ERC SED, and we compare these trends with those obtained applying Equation (7) to the data of Table 13. Figure 36 shows the location of HSP objects (blue solid boxes), ISPs/LSPs objects (orange solid boxes) and FSRQs (red solid circles).
The values of γSSCpeak estimated for the case of SSC emission (dashed blue line with stars) show clearly the effect of the transition from the TH to the KN regime. We note that all but two of the HBLs, lie below the νSpeak ∝ γSpeak line. In particular all the HSP objects below the νSpeak ∝ γSpeak line have γpeak values below the prediction of the SSC scenario (solid blue line). In contrast, all the FSRQs and the LSP/ISP BL Lacs but one lie above the νSpeak ∝ γSpeak line. The majority of the FSRQs objects have a value of γpeak in excess of a factor of ∼104 and limited by the prediction from the ERC model (purple dashed line with stars). The LBLs/IBLs sources are more uniformly distributed across the region delimited by the SSC TH prediction and by the ERC one. By further dividing the sample in Compton dominated (CD) objects (νICpeak F(νICpeak) > 2 νSpeak F(νSpeak)) and non-Compton dominated (NCD) objects (νICpeak F(νICpeak) ⩽ 2 νSpeak F(νSpeak)), we found that all the CD objects lie above the νSpeak ∝ γSpeak line and populate the region between the SSC TH and the ERC regime, with the FSRQs clustering toward the ERC region.
Our analysis shows that the ERC model could explain the high CD values as well as the high values of γSSCpeak estimated in the case of FSRQs and ISP/LSP BL Lacs. In order to explain the high values of γSSCpeak obtained in the case of FSRQs in the context of single zone SSC emission model, a very small value of the magnetic field with (B < 0.01 G) is required.
As a final step, we discuss two additional effects that have consequences for the source distribution in this parameter space:
- 1.The Bδ degeneracy on γSpeak can affect the transition region from the TH to KN regime, since high values of δ allow the TH regime to propagate toward higher frequencies.
- 2.The values of γpeak in the case of a UV external radiation field (purple line Figure 36) constitute an upper limit to the observed values of γpeak, meaning that objects in the region below the ERC prediction line require a wider range of external photon energies, extending down to the IR band.
To take into account both these effects we perform Monte Carlo (MC) simulations. Specifically, we generate both the SSC and ERC numerical computation of the SED extracting δ, B, and the temperature of the accretion disk T from a random uniform distribution in order to cover a larger volume of the parameter space. We generate 1000 realizations, with δ ranging in the interval (10–15), B in the interval (0.01–1) G, and T in the interval (10–104.5) K. In Figure 36, the MC results for the case of SSC fall within the area delimited by the blue contour line, while the results in the case of the ERC model are delimited by the light red contour line.
We note that the MC simulations, compared to the ERC one for the only case of UV external photons (purple line), cover a much wider region of the parameter space. In the case of the MC SED, the range of temperatures of the BB emission allows us to take into account external photon fields peaking at IR frequencies. The resulting MC realizations populate the whole parameter space delimited by the ERC/UV (purple line) and the SSC/TH case (solid blue line, below about 1015 Hz). This suggests that in the ERC paradigm, the observed data, FSRQs (red circles), and ISP/LSP BL Lacs (orange square symbols), require external photon fields ranging form the UV down to the IR.
An alternative scenario that can explain the distribution of LBAS blazars in the plot of Figure 36 advocates the superposition of two or more SSC components with different intrinsic energetics reflecting different conditions of the associated components. Such composition of multiple relativistic plasmoids predicts that the large γ-ray excess, over a simple SSC model, observed in many LSP blazars in Figure 36, and the flat or concave shape of the γ-ray SED of a number of ISP/HSP blazars (see e.g., 3C66A, Figure 3, PKS 0447-439, Figure 6, 1ES 0502+675, Figure 7, and PG 1246+586, Figure 15) is the result of the presence of a second (or higher order) SSC component that is subdominant in the low-ν (radio-IR) range but emerges at higher energies, after the synchrotron peak of the first, less energetic, component (see, e.g., the case of S5 0716+714; Giommi et al. 2008). The combination of these multiple components is consistent with the intensity and spectral variability observed in these blazars. In such a model, the SED of HBL-type sources can be fitted with a primary SSC component which peaks at the IR/optical (S) and γ-ray band (IC), and with a second more energetic and usually more variable component, which peaks in the UV or X-ray band (S) and at ≈GeV energies (IC) thus explaining the widespread variability of these sources at TeV energies.
The predictions of this last model are quite different from those of the ERC model and can therefore be tested by future multifrequency observation campaigns. A specific discussion of the details of such a multi-component SSC model will be presented in a dedicated paper.
8. SUMMARY AND CONCLUSION
We have carried out a detailed investigation of the broadband (radio to high-energy γ-ray) spectral properties of the LBAS sample of Fermi bright blazars using a large number of multi-frequency simultaneous observations as well as literature and archival data. Using data obtained with Fermi, Swift, radio/millimeter telescopes, infra-red, and optical facilities we have been able to assemble simultaneous or quasi-simultaneous SED of a sizable and representative fraction of a homogeneous sample of blazars detected during a γ-ray all sky survey and not under special circumstances such as strong flaring activity. This collection of high-quality, well-sampled, nearly simultaneous, broadband SED for a large number of blazars is unprecedented and allowed us to estimate a number of important parameters characterizing the SED of γ-ray selected blazars and to address some key aspects of blazar demographics and physics. Our main results are as follows.
- 1.We derived reliable estimates of the frequency of the synchrotron (νSpeak) and of the inverse Compton peaks (νICpeak) for over 100 LBAS blazars. This was done directly from the simultaneous data for the 48 sources for which we have the SED (see Figures 1–24). For the remaining ones, νSpeak and νICpeak were estimated indirectly using a refined version of the method of Padovani & Giommi (1995) based on the position in the αox–αro plane, for the former, and on the slope of the γ-ray spectrum for the latter, as the γ-ray spectral slope and νICpeak are strongly correlated (see Figure 29). The determination of νSpeak for the large majority of the sources in the sample prompted us to develop a new SED-based classification scheme for all non-thermal dominated AGNs based on an extension of the classification previously used for BL Lac objects only (see Section 6). We also find that the γ-ray spectral slope is strongly correlated with the slope of the X-ray spectrum (see Figure 35). Such a correlation is expected at first order in synchrotron-inverse Compton scenarios; however, the expected spectral slopes in the two energy bands depend on the position of the Synchrotron (e.g., Padovani & Giommi 1996) and inverse Compton peaks broadening the correlation.
- 2.Considering that (a) all the γ-ray sources in the bright sample of Fermi blazars that have been associated with radio loud AGNs (Abdo et al. 2009a, 2009b) have αox and αro similar to those of previously known blazars (see Figure 27); (b) that among the only seven still unidentified sources with Galactic latitude |b|>10°, two are likely blazars (similar to the ones already identified as the γ-ray error region includes radio-optical candidates with αox ≳ 1.4 and αro ∼0.5) and that the error region of the remaining five do not include any radio candidates brighter than 3 mJy, we can conclude that γ-ray selected blazars have broadband spectral properties similar to those of radio and X-ray discovered blazars implying that they are all drawn from the same underlying population. No evidence was found for the hypothetical class of UHBLs (see Ghisellini 1999; Giommi et al. 2001; Nieppola et al. 2006) characterized by a synchrotron emission that is so energetic as to reach the γ-ray band, and thus populate the extreme part of the αox–αro diagram defined by 0.2 < αro < 0.4 and αox ≲ 0.7 (see Figure 27). These sources, if bright and existing in good numbers, should have been found in a γ-ray survey such as LBAS, just as the population of HBL BL Lacs was discovered when X-ray surveys became available. Alternatively, UHBLs could be intrinsically weak γ-ray sources and/or mis-identified (Costamante et al. 2007) and their discovery must await the availability of much deeper samples than LBAS.
- 3.The distribution of the synchrotron peak frequency is very different for the FSRQ and BL Lac subsamples with values of νSpeak located between 1012.5 and 1014.5 Hz in FSRQ and between 1013 and 1017 Hz in BL Lacs (see Figure 31). This result rules out the existence of FSRQs of the HSP type (HBL in the old BL Lac nomenclature), consistent with what was also observed in radio, microwave, and X-ray surveys. The much larger νSpeak values that can be reached by BL Lacs explain their observed harder γ-ray spectral slopes and hence the much better sensitivity of the LAT instrument to these sources (see Figure 7 of Abdo et al. 2009b). This selection effect will be even stronger above a few GeV and fits with the well-known fact that TeV detected blazars are almost exclusively of the HSP (HBL) type. This also reproduces the case of the soft X-ray band where HSB BL Lacs (HBLs) are the dominant type of blazars.
- 4.A remarkable difference between LSP and HSP sources (see Section 6) is that more than 50% (10/16) of the HSP blazars with radio flux larger than 300 mJy at 1.4 GHz, in the BZCat catalog are detected in the LBAS sample while this fraction goes down to only ≲13% (58/452) for LSP blazars with radio flux larger than 500 mJy at 1.4 GHz. Note that the sample of undetected LBL blazars has similar overall properties than that of the detected ones, e.g., 〈z〉detected = 1.0, 〈z〉undetected = 1.1, 〈Vmag〉detected = 17.1 and 〈Vmag〉undetected = 17.7. However, some authors (e.g., Kovalev et al. 2009; Lister et al. 2009; Pushkarev et al. 2009; Kovalev 2009; Savolainen et al. 2010) showed that the LAT detected blazars might have larger Doppler boosting factors than undetected ones. A detailed comparison of all important parameters of γ-ray detected and undetected blazars will be done when the much larger catalog of γ-ray sources based on approximately one year of LAT data is available.
- 5.The minimum νSpeak of BL Lac objects of ∼1013 Hz is consistent with the results of Maselli et al. (2010) who conducted a careful search for very low synchrotron peaked BL Lac objects among the over 2000 blazars of the BZcat list and found them to be very rare or non-existent. The fact that the BL Lac minimum νSpeak appears to be larger than in FSRQs could be due to some intrinsic difference in the mechanism of particle acceleration in the two types of blazars or to a mere selection effect. In fact, the non-thermal emission of very low νSpeak BL Lacs would be minimal in the optical band (see Figure 30) causing them to be classified more easily as FSRQs rather than BL Lacs if low intensity broad lines (which would normally be below the non-thermal continuum) are present in this type of objects.We note that for LSP sources (νSpeak <1014 Hz), the ratio of γ-ray detected FSRQs compared to BL Lacs is approximately four, i.e., a value similar to that seen in the radio and microwave bands (∼6 both in the 1 Jy and in the WMAP3 samples; Stickel et al. 1991; Giommi et al. 2009). This strongly suggests that the mechanism that produces γ-rays is, at first order, the same in both LBL FSRQs and BL Lacs (see also Giommi et al. 2009).
- 6.The results of this study lead to the conclusion that a simple homogeneous, one-zone, SSC model cannot explain the SED of the majority of the detected sources, especially of the LBL type (see Figure 36). In addition, differential variability in the simultaneous optical and X-ray data observed in IBL and HBL objects (that is, close to the peak of the synchrotron component) suggests that multiple components are present in non-LBL blazars (e.g., S5 0716+714; Giommi et al. 2008), as also clearly shown by simultaneous X-ray/TeV campaigns (e.g., PKS 2155-304; Aharonian et al. 2009). Our results also show that ERC models can easily fit the data as they can cover a very wide part of the parameter space of Figure 36 (orange squares). However, models that are based on the presence of external radiation fields that are significantly different in FSRQs and BL Lacs, such as the broad-line region, accretion disk etc., must explain why (a) the ratio of the number of FSRQs and BL Lacs of the LBL type (which have similar γ-ray spectral slopes and therefore are affected in the same way by the higher LAT sensitivity to hard sources) is similar in radio/microwave selected samples (e.g., 1 Jy, WMAP) and in the LBAS γ-ray selected sample, and (b) why BL Lacs appear to show equal, or even larger, values of γSSCpeak (that is larger γ-ray excess above SSC) than FSRQs in Figure 36. Finally, any emission model should explain why only less than 13% of bright radio sources (F > 0.5 Jy at 1.4 GHz) of the LBL type are in the LBAS sample, while the other 87% with similar observational properties are below the LBAS detection threshold and may well be radiating close to simple SSC. We intend to address these topics in future papers.
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Standard image High-resolution imageThe Fermi-LAT Collaboration acknowledges the generous support of a number of agencies and institutes that have supported the Fermi-LAT Collaboration. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK), and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council, and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase from the following agencies is also gratefully acknowledged: the Istituto Nazionale di Astrofisica in Italy and the K. A. Wallenberg Foundation in Sweden. This research is based also on observations with the 100 m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. RATAN-600 observations are supported in part by the Russian Foundation for Basic Research (projects 01-02-16812 and 08-02-00545). Part of this work was supported by Georgian National Science Foundation grant GNSF/ST-08/4-404 The mid-infrared VISIR results are based on observations carried out at the European Southern Observatory under programmes ID 078.B-0366, 079.B-0448, and 081.B-0404. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. St. Petersburg University team acknowledges support from Russian RFBR foundation via grant 09-02-00092. AZT-24 observations are made within an agreement between Pulkovo, Rome, and Teramo observatories. We acknowledge the use of data and software facilities from the ASDC, managed by the Italian Space Agency (ASI). Part of this work is based on archival data and on bibliographic information obtained from the NASA/IPAC Extragalactic Database (NED) and from the Astrophysics Data System (ADS).
Facilities: Effelsberg - Effelsberg Radio Telescope, Fermi - Fermi Gamma-Ray Space Telescope (formerly GLAST), OVRO:40m - Owens Valley Radio Observatory's 40 meter Telescope, Swift - Swift Gamma-Ray Burst Mission, WEBT - Whole Earth Blazar Telescope
APPENDIX: UNFOLDING ANALYSIS
The purpose of the unfolding method is to estimate the true distribution (in this case the true source energy spectrum), given the observed one and assuming the knowledge of the smearing matrix, which describes the migration effects among the energy bins as well as the efficiencies (Mazziotta 2009). The smearing matrix is evaluated using the Monte Carlo package Gleam, a Geant4 based simulation code of the instrument (Atwood et al. 2009), and taking into account the pointing history of the source under investigation. The unfolding analysis is performed selecting, from the initial data samples, events in an energy-dependent RoI centered on the position of the source under investigation. The maximum allowed angular separation of the events selected from the source position is a decreasing function of energy that reproduces the behavior of the PSF of the LAT. Events entering the LAT with a zenith angle larger than 105° with respect to the Earth reference frame and with an angle larger than 664 with respect to the Z-axis in the instruments reference frame have been also excluded from this analysis. The observed spectrum built from the data selected according to the procedure described above includes the background contributions, that have to be subtracted before performing the unfolding. In the examples shown in Figures 37 and 38, the background counts have been evaluated from real data, considering the photons in an annulus external to the analysis RoI and rescaling them in each observed energy bin for the ratio between solid angles and live times. Once the source spectrum has been unfolded from the observed one, both statistical and systematic errors on the observed energy distribution can be easily propagated to the unfolded spectrum. In Figures 37 and 38, a comparison between the SED obtained with the unfolding and the spectra obtained with gtlike is shown for the blazars 3C454.3 and ASO0235+164. The unfolded spectra are consistent with the ones obtained from gtlike.
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Standard image High-resolution imageFootnotes
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Average flux densities were calculated on the one day binned data sets, to avoid giving too much weight to the days with denser sampling.
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