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Title: Evidence for large temperature fluctuations in quasar accretion disks from spectral variability

The well-known bluer-when-brighter trend observed in quasar variability is a signature of the complex processes in the accretion disk and can be a probe of the quasar variability mechanism. Using a sample of 604 variable quasars with repeat spectra in the Sloan Digital Sky Survey-I/II (SDSS), we construct difference spectra to investigate the physical causes of this bluer-when-brighter trend. The continuum of our composite difference spectrum is well fit by a power law, with a spectral index in excellent agreement with previous results. We measure the spectral variability relative to the underlying spectra of the quasars, which is independent of any extinction, and compare to model predictions. We show that our SDSS spectral variability results cannot be produced by global accretion rate fluctuations in a thin disk alone. However, we find that a simple model of an inhomogeneous disk with localized temperature fluctuations will produce power-law spectral variability over optical wavelengths. We show that the inhomogeneous disk will provide good fits to our observed spectral variability if the disk has large temperature fluctuations in many independently varying zones, in excellent agreement with independent constraints from quasar microlensing disk sizes, their strong UV spectral continuum, and single-band variability amplitudes. Our resultsmore » provide an independent constraint on quasar variability models and add to the mounting evidence that quasar accretion disks have large localized temperature fluctuations.« less
Authors:
; ;  [1] ;  [2]
  1. Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
  2. Departments of Physics and Astronomy, University of California, Berkeley, CA 94720 (United States)
Publication Date:
OSTI Identifier:
22351565
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 783; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; AMPLITUDES; COMPARATIVE EVALUATIONS; FLUCTUATIONS; FORECASTING; LIMITING VALUES; QUASARS; SPECTRA; TEMPERATURE MONITORING