Journal
ASTROPHYSICAL JOURNAL
Volume 642, Issue 1, Pages 87-95Publisher
IOP PUBLISHING LTD
DOI: 10.1086/500919
Keywords
accretion, accretion disks; quasars : general; ultraviolet : general
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Using Sloan Digital Sky Survey (SDSS) QSO spectra taken at multiple epochs, we find that the composite flux differences in the rest-frame wavelength range 1300-6000 angstrom can be fit by a standard thermal accretion disk model in which the accretion rate has changed from one epoch to the next ( without considering additional continuum emission components). The fit to the composite residual has two free parameters: a normalizing constant and the average characteristic temperature (T) over bar*. In turn, in a standard disk the characteristic temperature is dependent on the ratio of the mass accretion rate to the square of the black hole mass. Therefore, provided enough time has elapsed for a composite disk spectrum to adjust to a new average characteristic temperature, reasonably consistent with the standard model, we conclude that most of the UV-optical variability observed in QSOs may be due to processes involving changes in disk accretion rates. This is consistent with the conclusion that a significant fraction of a QSO's UV-optical spectrum comes directly from the disk.
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