Optical variability of quasars: A damped random walk

Željko Ivezić, Chelsea Macleod

Research output: Chapter in Book/Report/Conference proceedingConference contribution


A damped random walk is a stochastic process, defined by an exponential covariance matrix that behaves as a random walk for short time scales and asymptotically achieves a finite variability amplitude at long time scales. Over the last few years, it has been demonstrated, mostly but not exclusively using SDSS data, that a damped random walk model provides a satisfactory statistical description of observed quasar variability in the optical wavelength range, for rest-frame timescales from 5 days to 2000 days. The best-fit characteristic timescale and asymptotic variability amplitude scale with the luminosity, black hole mass, and rest wavelength, and appear independent of redshift. In addition to providing insights into the physics of quasar variability, the best-fit model parameters can be used to efficiently separate quasars from stars in imaging surveys with adequate long-term multi-epoch data, such as expected from LSST.

Original languageEnglish
Title of host publicationProceedings of the International Astronomical Union
PublisherCambridge University Press
Number of pages4
ISBN (Print)9781107045248
Publication statusPublished - 2014

Publication series

NameProceedings of the International Astronomical Union
ISSN (Print)17439213
ISSN (Electronic)17439221


  • galaxies: active
  • quasars: general
  • stars: statistics
  • stars: variables
  • surveys

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