Affiliation:
1. Cosmic Dawn Center (DAWN)
2. Niels Bohr Institute, University of Copenhagen, Jagtvej 128, DK-2200 Copenhagen, Denmark
3. SUPA School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK
Abstract
ABSTRACT
We present a study of 9 242 spectroscopically confirmed quasars with multiepoch ugriz photometry from the SDSS Southern Survey. By fitting a separable linear model to each quasar’s spectral variations, we decompose their five-band spectral energy distributions into variable (disc) and non-variable (host galaxy) components. In modelling the disc spectra, we include attenuation by dust on the line of sight through the host galaxy to its nucleus. We consider five commonly used attenuation laws, and find that the best description is by dust similar to that of the Small Magellanic Cloud, inferring a lack of carbonaceous grains from the relatively weak 2175-Å absorption feature. We go on to construct a composite spectrum for the quasar variations spanning 700–8000 Å. By varying the assumed power-law Lν ∝ να spectral slope, we find a best-fitting value α = 0.71 ± 0.02, excluding at high confidence the canonical Lν ∝ ν1/3 prediction for a steady-state accretion disc with a T ∝ r−3/4 temperature profile. The bluer spectral index of the observed quasar variations instead supports the model of Agol & Krolik, and Mummery & Balbus, in which a steeper temperature profile, T ∝ r−7/8, develops as a result of finite magnetically induced stress at the innermost stable circular orbit extracting energy and angular momentum from the black hole spin.
Funder
Danish National Research Foundation
European Research Council
STFC
Alfred P. Sloan Foundation
National Science Foundation
U.S. Department of Energy
National Aeronautics and Space Administration
Max Planck Society
Higher Education Funding Council for England
American Museum of Natural History
University of Basel
Case Western Reserve University
University of Chicago
Drexel University
Institute for Advanced Study
Johns Hopkins University
Los Alamos National Laboratory
New Mexico State University
Ohio State University
University of Pittsburgh
University of Portsmouth
Princeton University
United States Naval Observatory
University of Washington
Publisher
Oxford University Press (OUP)
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
4 articles.
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