We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 quasars for which the spectral energy distributions include X-ray spectral indices and UV data. Of these, 29 are radio quiet, and 18 are radio loud. The SEDs are presented both in figures and in tabular form, with additional tabular material published on CD-ROM. Previously unpublished observational data for a second set of quasars excluded from the primary sample are also tabulated. The effects of host galaxy starlight contamination and foreground extinction on the UVSX sample are considered and the sample is used to investigate the range of SED properties. Of course, the properties we derive are influenced strongly by the selection effects induced by quasar discovery techniques. We derive the mean energy distribution (MED) for radio-loud and radio-quiet objects and present the bolometric corrections derived from it. We note, however, that the dispersion about this mean is large (-one decade for both the infrared and ultraviolet components when the MED is normalized at the near-infrared inflection). At least part of the dispersion in the ultraviolet may be due to time variability, but this is unhkely to be important in the infrared. The existence of such a large dispersion indicates that the MED reflects only some of the properties of quasars and so should be used only with caution. Subject headings: atlases-galaxies: photometry-quasars: general

We analyze a sample of optical light curves for 100 quasars, 70 of which have black hole mass estimates. Our sample is the largest and broadest used yet for modeling quasar variability. The sources in our sample have z < 2.8, 10 42 λL λ (5100Å) 10 46 , and 10 6 M BH /M ⊙ 10 10 . We model the light curves as a continuous time stochastic process, providing a natural means of estimating the characteristic time scale and amplitude of quasar variations. We employ a Bayesian approach to estimate the characteristic time scale and amplitude of flux variations; our approach is not affected by biases introduced from discrete sampling effects. We find that the characteristic time scales stongly correlate with black hole mass and luminosity, and are consistent with disk orbital or thermal time scales. In addition, the amplitude of short time scale variations is significantly anti-correlated with black hole mass and luminosity. We interpret the optical flux fluctuations as resulting from thermal fluctuations that are driven by an underlying stochastic process, such as a turbulent magnetic field. In addition, the intranight variations in optical flux implied by our empirical model are 0.02 mag, consistent with current microvariability observations of radio-quiet quasars. Our stochastic model is therefore able to unify both long and short time scale optical variations in radio-quiet quasars as resulting from the same underlying process, while radio-loud quasars have an additional variability component that operates on time scales 1 day.

We report the discovery of the progenitor of the recent Type IIn SN 2008S in the nearby galaxy NGC 6946. Surprisingly, it was not found in deep, preexplosion optical images of its host galaxy taken with the Large Binocular Telescope, but only through examination of archival Spitzer mid-IR data. A source coincident with the SN 2008S position is clearly detected in the 4.5, 5.8, and 8.0 mm IRAC bands, showing no evident variability in the 3 years prior to the explosion, yet is undetected at 3.6 and 24 mm. The distinct presence of ∼440 K dust, along with stringent LBT limits on the optical fluxes, suggests that the progenitor of SN 2008S was engulfed in a shroud of its own dust. The inferred luminosity of ≈3.5 # 10 4 L , implies a modest mass of ∼10 M . We , conclude that objects like SN 2008S are not exclusively associated with the deaths or outbursts of very massive h Carinae-like objects. This conclusion holds based solely on the optical flux limits even if our identification of the progenitor with the mid-IR source is incorrect.

Moderate resolution data for 40 quasi-stellar objects (QSOs) at z ≈ 2 were combined with spectra of comparable resolution of 59 QSOs with redshifts greater than 1.7 found in the literature to form a large, homogeneous sample of moderate resolution (∼1Å) QSO spectra. These spectra were presented and the statistics of the Lyman α forest were discussed in Paper I. In this analysis, we demonstrate that a proximity effect is present in the data, ie. there exists a significant (5.5σ) deficit of lines at z abs ≈ z em . Within 1.5 h −1 Mpc of the QSO emission redshift, the significance does depend on QSO luminosity, in accordance with the theory that this effect is caused by enhanced ionization of hydrogen in the vicinity of the QSO from UV photons from the QSO itself. The photoionization model of Bajtlik, Duncan, & Ostriker permits an estimate of the mean intensity of the extragalactic background radiation at the Lyman limit. We compare the results of this standard analysis with those obtained using a maximum likelihood technique. If the spectrum of the background is assumed to be identical to that of each individual QSO, and if this background is assumed to be constant over the redshift range 1.7 < z < 3.8, then the best fit value for J(ν 0 ) is found to be 1.4 +1.1 −0.5 × 10 −21 ergs s −1 cm −2 Hz −1 sr −1 , using QSO redshifts based on the Lyα emission line. Systemic QSO redshifts based on the [OIII] λ5007 emission line for 19 objects in our sample show an average redshift of ∼400 km s −1 with respect to Lyα emission. Using redshifts based on [OIII] or Mg II for the 35 objects for which they are measured and adding 400 km s −1 to the remaining QSO Lyα redshifts gives a lower value of J(ν 0 ), 7.0 +3.4 −4.4 × 10 −22 ergs s −1 cm −2 Hz −1 sr −1 . This value is in reasonable agreement with the predictions of various models of the ionizing background based on the integrated QSO luminosity function. Allowing for the fact that individual QSOs have different spectral indicies which may also be different from that of the background, we use the standard methods to solve for the HI photoionization rate, Γ, and the parameters describing its evolution with redshift. The best fit value for the HI ionization rate we derive is 1.9 +1.2 −1.0 × 10 −12 s −1 , in good agreement with models of the background which incorporate QSOs only. Finally, we use simulated Lyman α forest spectra including the proximity effect to investigate curve-of-growth effects in the photoionization model used in the analysis. We find that the presence of lines on the saturated part of the curve-of-growth could cause our estimates of the background intensity to be overestimated by a factor of two to three. This large absorption line sample and these techniques for measuring the background and understanding the systematics involved allow us to place what we believe are the firmest limits on the background at these redshifts.

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