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

Brian C. WilhiteCurrent address: Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801Daniel E. Vanden BerkDepartment of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802Richard G. KronDepartment of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637Donald P. SchneiderDepartment of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802Nicholas PereyraDepartment of Physics and Astronomy, University of Pittsburgh, 100 Allen Hall, 3941 O'Hara Street, Pittsburgh, PA 15260Robert J. BrunnerDepartment of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801Gordon T. RichardsPrinceton University Observatory, Peyton Hall, Princeton, NJ 08544Jonathan V. Brinkmann

2005en

ABI

Аннотация

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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DOI: 10.1086/430821

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