Dust and the intrinsic spectral index of quasar variations: hints of finite stress at the innermost stable circular orbit
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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jan 29, 2022
- Source ID
- 10.1093/mnras/stac248
Entities
People
- John R. Weaver
- Keith Horne
Organizations
- Alfred P. Sloan Foundation
- American Museum of Natural History
- Case Western Reserve University
- Cosmic Dawn Center
- Danish National Research Foundation
- Drexel University
- European Research Council
- Higher Education Funding Council for England
- Institute for Advanced Study
- Johns Hopkins University
- Los Alamos National Laboratory
- Max Planck Society
- National Aeronautics and Space Administration
- National Science Foundation
- New Mexico State University
- Ohio State University
- Princeton University
- Science and Technology Facilities Council
- United States Department of Energy
- United States Naval Observatory
- University of Basel
- University of Chicago
- University of Copenhagen
- University of Pittsburgh
- University of Portsmouth
- University of St Andrews
- University of Washington