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D.E. Vanden Berk (Pittsburgh), B.C. Wilhite, R.G. Kron (Chicago), SDSS Collaboration
Using a sample of over 25000 spectroscopically confirmed quasars from the Sloan Digital Sky Survey, we show how quasar variability in the optical/UV regime depends upon time lag, luminosity, rest wavelength, redshift, the presence of radio and X-ray emission, and the presence of broad absorption line systems. The time dependence of variability (the structure function) is well-fit by a single power-law on timescales from days to years. There is a strong anti-correlation with rest wavelength, and quasars are systematically bluer when brighter at all redshifts. There is an anti-correlation of variability with quasar luminosity, which is modulated by the presence of host galaxy light at low redshifts. After accounting for these dependencies, there remains a weak but significant correlation of variability with redshift, indicating evolution of the quasar population or the variability mechanism. We parameterize all of these relationships. We also find that quasars with FIRST radio detections are more variable than their radio-silent counterparts, and quasars with RASS X-ray detections are much more variable than those without. We find no significant difference in the variability of quasars with and without broad absorption line troughs. Currently, no models of quasar variability address more than a few of these relationships, leaving a large number of constraints for quasar models in general.
Funding for the SDSS is provided by the Alfred P. Sloan Foundation, NASA, NSF, DOE, Monbukagakusho, the Max Planck Society and the member institutions. The SDSS web site is http://www.sdss.org/.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.