Quasar optical variability in the palomar-quest survey

Anne Bauer, Charles Baltay, Paolo Coppi, Nancy Ellman, Jonathan Jerke, David Rabinowitz, Richard Scalzo

Research output: Contribution to journalReview articlepeer-review

83 Scopus citations


The ensemble variability properties of nearly 23,000 quasars are studied using the Palomar-QUEST Survey. The survey has covered 15,000 deg2 multiple times over 3.5 years using seven optical filters, and has been calibrated specifically for variability work. Palomar-QUEST allows for the study of rare objects using multiple epochs of consistently calibrated, homogeneous data, obviating the common problem of generating comparable measurements from disparate data sets. A power-law fit to the quasar structure function versus time yields an index of 0.432 ± 0.024 for our best measured sample. We see the commonly reported anticorrelation between average optical variability amplitude and optical luminosity, and measure the logarithmic decrease in variability amplitude to scale as the logarithm of the luminosity times 0.205 ± 0.002. Black hole mass is positively correlated with variability amplitude over three orders of magnitude in mass. Quasar variability amplitude is seen to decrease with Eddington ratio as a step function with a transition around Eddington ratio of 0.5. The higher variability at low Eddington ratios is due to excess power at timescales shorter than roughly 300 days. X-ray and radio measurements exist for subsets of the quasar sample. We observe an anticorrelation between optical variability amplitude and X-ray luminosity. No significant correlation is seen between average optical variability properties and radio luminosity. The timescales of quasar fluctuations are suggestive of accretion disk instabilities. The relationships seen between variability, Eddington ratio, and radio and X-ray emission are discussed in terms of a possible link between the behavior of quasars and black hole X-ray binaries.

Original languageEnglish
Pages (from-to)1241-1256
Number of pages16
JournalAstrophysical Journal
Issue number2
StatePublished - May 10 2009


  • galaxies: active
  • quasars: general
  • techniques: photometric


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