Synoptic sky surveys and the diffuse supernova neutrino background: Removing astrophysical uncertainties and revealing invisible supernovae

Amy Lien (連雅琳), Brian D. Fields, and John F. Beacom

Phys. Rev. D 81, 083001 – Published 1 April 2010

Abstract

The cumulative (anti)neutrino production from all core-collapse supernovae within our cosmic horizon gives rise to the diffuse supernova neutrino background (DSNB), which is on the verge of detectability. The observed flux depends on supernova physics, but also on the cosmic history of supernova explosions; currently, the cosmic supernova rate introduces a substantial ( $\pm 40 %$ ) uncertainty, largely through its absolute normalization. However, a new class of wide-field, repeated-scan (synoptic) optical sky surveys is coming online, and will map the sky in the time domain with unprecedented depth, completeness, and dynamic range. We show that these surveys will obtain the cosmic supernova rate by direct counting, in an unbiased way and with high statistics, and thus will allow for precise predictions of the DSNB. Upcoming sky surveys will substantially reduce the uncertainties in the DSNB source history to an anticipated $\pm 5 %$ that is dominated by systematics, so that the observed high-energy flux thus will test supernova neutrino physics. The portion of the universe ( $z ≲ 1$ ) accessible to upcoming sky surveys includes the progenitors of a large fraction ( $≃ 87 %$ ) of the expected 10–26 MeV DSNB event rate. We show that precision determination of the (optically detected) cosmic supernova history will also make the DSNB into a strong probe of an extra flux of neutrinos from optically invisible supernovae, which may be unseen either due to unexpected large dust obscuration in host galaxies, or because some core-collapse events proceed directly to black hole formation and fail to give an optical outburst.

Received 28 January 2010

DOI:https://doi.org/10.1103/PhysRevD.81.083001

Authors & Affiliations

Amy Lien (連雅琳)¹, Brian D. Fields^1,2, and John F. Beacom^3,4,5

¹Department of Astronomy, University of Illinois, Urbana, Illinois 61801, USA
²Department of Physics, University of Illinois, Urbana, Illinois 61801, USA
³Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, Ohio 43210, USA
⁴Department of Physics, Ohio State University, Columbus, Ohio 43210, USA
⁵Department of Astronomy, Ohio State University, Columbus, Ohio 43210, USA

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Vol. 81, Iss. 8 — 15 April 2010

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Images

Figure 1
DSNB and synoptic survey redshift distributions. Upper panel: The integrand of Eq. (1) as a function of redshift for different choices of observed neutrino energies; this shows the redshift distribution of sources that contribute to the DSNB signal at these energies. Here we assume all the supernovae are core-collapse events, as defined in Sec. 1. Bottom panel: The blue curve is the supernova detection rate by LSST in $r$ band as a function of redshift, with survey depth $m_{\lim }^{sn} = 23^{mag}$ and sky coverage of 6.1 sr ( $20 000 \deg^{2}$ ). The black curve is a more conservative estimation of the LSST supernova detection rate by excluding Type IIn supernovae, which seem to be the most luminous based on the small sample of current data. The red curve is the fiducial supernova rate for comparison, which is the full-sky supernova rate without considering dust extinction or survey depth. The curves have bin size $Δ z = 0.05$ , and the band thickness (which is in most cases thinner than the curve width) represents the statistical uncertainty $1 / \sqrt{N}$ .Reuse & Permissions
Figure 2
Upper panel: Neutrino detection rate as a function of neutrino observed energy, with different neutrino effective temperatures, is plotted for comparison (curves from left to right represent 4, 6, 8 MeV, respectively). The band thickness of the curves represents a $δ R_{tot} / R_{tot} = 40 %$ uncertainty in the current CSNR normalization. Bottom panel: Same as the upper panel, but with a 5% normalization uncertainty instead, which is the uncertainty expected from upcoming supernova surveys with one year observations.Reuse & Permissions
Figure 3
Summary of current and future constraints on the invisible supernova rate $R_{invis}$ (i.e. the direct-collapse event rate in our assumption) and the visible supernova rate $R_{vis}$ (i.e. the core-collapse event rate in our assumption). Blue regions are those allowed by current observed cosmic star-formation rate (CSFR) and CSNR and their uncertainties. The grey-lined region is disallowed based on the nondetection of the DSNB by Super-K with the assumption that $T_{ν} = 4 MeV$ for visible events and 7.5 MeV (and also a higher total energy) for invisible events. Another DSNB limit with $T_{ν} = 6 MeV$ instead of 4 MeV is also plotted for comparison. The horizontal dashed line shows the sensitivity to stellar disappearance, which will directly probe the invisible supernova rate [58]. Note circles explored in Fig. 4 and stars in Fig. 5. The square marks a baseline shown in Figs. 4, 5.Reuse & Permissions
Figure 4
One year neutrino detection as a function of neutrino observed energy. Three different fractions of the invisible events are plotted with $R_{tot}$ fixed to the fiducial number. Curves with different colors correspond to the square/circles with the same color in Fig. 3, i.e., red (top) curve represents $f_{invis} = 40 %$ , purple (middle) curve represents $f_{invis} = 10 %$ , and black (bottom) curve represents $f_{invis} = 0 %$ . The band thickness of the curves represents 5% uncertainty expected from upcoming supernova surveys.Reuse & Permissions
Figure 5
Similar to Fig. 4. However, we allow larger numbers for $R_{tot}$ . Curves with different colors correspond to square/stars in Fig. 3, i.e., orange (top) curve represents $f_{invis} = 50 %$ , red (second top) curve represents $f_{invis} = 17 %$ , purple (third top) curve represents $f_{invis} = 10 %$ , and black (bottom) curve represents $f_{invis} = 0 %$ . The band thickness of the curves represents 5% uncertainty expected from upcoming supernova surveys.Reuse & Permissions
Figure 6
Upper panel: Extreme lower bounds to the DSNB detection rate obtained by summing supernovae observed by surveys with different limiting magnitudes, the blue curve is the limiting magnitude proposed by LSST and Pan-STARRS. The blue and red curves represent a lower limit because they apply no correction for supernovae that are too dim or too obscured to be seen in surveys. The two black curves are shown for comparison: The top black curve is the DSNB flux from all core-collapse events in the universe out to redshift $z \sim 6$ . The second top black curve is the DSNB flux from core-collapse events after considering dust obscuration but with infinite survey limiting magnitude. Results assume $T_{ν} = 4 MeV$ . Middle panel: The integrated DSNB detection rate, i.e. the detection rate above a certain antineutrino energy and integrated out to $ϵ_{ν} = 30 MeV$ . The colors indicate the same features as in the top plot. Lower panel: The fraction of the DSNB detection rate from the observed core-collapse events over those from the total collapse events. That is, a middle-panel red/blue curve divided by the highest black curve. Note that in this figure the $x$ axis starts at 2 MeV because no events can be detected below the threshold energy of 1.8 MeV.Reuse & Permissions

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