Constraining the Black Hole Mass and Accretion Rate in the Narrow-Line Seyfert 1 Galaxy RE J1034+396

We present a comprehensive study of the spectrum of the narrow-line Seyfert 1 (NLS1) galaxy RE J1034+396, summarizing the information obtained from the optical to X-rays with observations from the William Herschel 4.2 m Telescope, the Hubble Space Telescope, the Extreme Ultraviolet Explorer, ROSAT, ASCA, and BeppoSAX. The BeppoSAX spectra reveal a soft component which is well represented by two blackbodies with kT_eff = 60 and 160 eV, mimicking that expected from a hot, optically thick accretion disk around a low-mass black hole. This is borne out by our modeling of the optical-to-X-ray nuclear continuum, which constrains the physical parameters of a NLS1 for the first time. The models demonstrate that RE J1034+396 is likely to be a system with a nearly edge-on accretion disk (60°-75° from the disk axis), accreting at nearly Eddington rates (0.3-0.7L_Edd) onto a low-mass black hole (M_bh ~ 2-10 × 10⁶ M_☉). This is consistent with the hypothesis that NLS1s are Seyfert-scale analogies of galactic black hole candidates. The unusually high temperature of the big blue bump reveals a flat power-law-like continuum in the optical/UV which is consistent with an extrapolation to the hard X-ray power law, and which we speculate may be similar to the continuum component observed in BL Lac objects in their quiescent periods. From the BeppoSAX and ASCA data, we find that the slope of the hard X-ray power law depends very much on the form of the soft component which is assumed. For our best-fitting models, it lies somewhere between α = 0.7 and 1.3 and thus may not be significantly softer than active galactic nuclei in general.