Spectral Variability of Quasars in the Sloan Digital Sky Survey. I: Wavelength Dependence

Details Spectral Variability of Quasars in the Sloan Digital Sky Survey. I: Wavelength Dependence Spectral Variability of Quasars in the Sloan Digital Sky Survey. I: Wavelength Dependence

2005-04-13

arxiv.org/abs/astro-ph/0504309v1

Astrophys.J. 633 (2005) 638-648

Astronomy and Astrophysics

Astrophysics

47 pages, 14 figures, 3 tables, accepted for publication in ApJ

Scientific paper

10.1086/430821

Sloan Digital Sky Survey (SDSS) repeat spectroscopic observations have resulted in multiple-epoch spectroscopy for roughly 2500 quasars observed more than 50 days apart. From this sample, we identify 315 quasars that have varied significantly between observations. We create an ensemble difference spectrum (bright phase minus faint phase) covering rest-frame wavelengths from 1000 to 6000 Angstroms. This average difference spectrum is bluer than the average single-epoch quasar spectrum; a power-law fit to the difference spectrum yields a spectral index alpha_lambda = -2.00, compared to an index of alpha_lambda = -1.35 for the single-epoch spectrum. The strongest emission lines vary only 30% as much as the continuum. Due to the lack of variability of the lines, measured photometric color is not always bluer in brighter phases, but depends on redshift and the filters used. Lastly, the difference spectrum is bluer than the ensemble quasar spectrum only for lambda_rest < 2500 Angstroms, indicating that the variability cannot result from a simple scaling of the average quasar spectrum.

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