The color variability of quasars

Kasper B. Schmidt, Hans Walter Rix, Joseph C. Shields, Matthias Knecht, David W. Hogg, Dan Maoz, Jo Bovy

    Research output: Contribution to journalArticle

    Abstract

    We quantify quasar color variability using an unprecedented variability database-ugriz photometry of 9093 quasars from Sloan Digital Sky Survey (SDSS) Stripe 82, observed over 8 years at ∼60 epochs each. We confirm previous reports that quasars become bluer when brightening. We find a redshift dependence of this blueing in a given set of bands (e.g., g and r), but show that it is the result of the flux contribution from less-variable or delayed emission lines in the different SDSS bands at different redshifts. After correcting for this effect, quasar color variability is remarkably uniform, and independent not only of redshift, but also of quasar luminosity and black hole mass. The color variations of individual quasars, as they vary in brightness on year timescales, are much more pronounced than the ranges in color seen in samples of quasars across many orders of magnitude in luminosity. This indicates distinct physical mechanisms behind quasar variability and the observed range of quasar luminosities at a given black hole mass - quasar variations cannot be explained by changes in the mean accretion rate. We do find some dependence of the color variability on the characteristics of the flux variations themselves, with fast, low-amplitude, brightness variations producing more color variability. The observed behavior could arise if quasar variability results from flares or ephemeral hot spots in an accretion disk.

    Original languageEnglish (US)
    Article number147
    JournalAstrophysical Journal
    Volume744
    Issue number2
    DOIs
    StatePublished - Jan 10 2012

    Fingerprint

    quasars
    color
    accretion
    luminosity
    brightness
    hot spot
    timescale
    accretion disks
    flares
    photometry
    time measurement

    Keywords

    • accretion
    • accretion disks
    • galaxies: active
    • galaxies: nuclei
    • quasars: emission lines
    • quasars: general

    ASJC Scopus subject areas

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

    Schmidt, K. B., Rix, H. W., Shields, J. C., Knecht, M., Hogg, D. W., Maoz, D., & Bovy, J. (2012). The color variability of quasars. Astrophysical Journal, 744(2), [147]. https://doi.org/10.1088/0004-637X/744/2/147

    The color variability of quasars. / Schmidt, Kasper B.; Rix, Hans Walter; Shields, Joseph C.; Knecht, Matthias; Hogg, David W.; Maoz, Dan; Bovy, Jo.

    In: Astrophysical Journal, Vol. 744, No. 2, 147, 10.01.2012.

    Research output: Contribution to journalArticle

    Schmidt, KB, Rix, HW, Shields, JC, Knecht, M, Hogg, DW, Maoz, D & Bovy, J 2012, 'The color variability of quasars', Astrophysical Journal, vol. 744, no. 2, 147. https://doi.org/10.1088/0004-637X/744/2/147
    Schmidt KB, Rix HW, Shields JC, Knecht M, Hogg DW, Maoz D et al. The color variability of quasars. Astrophysical Journal. 2012 Jan 10;744(2). 147. https://doi.org/10.1088/0004-637X/744/2/147
    Schmidt, Kasper B. ; Rix, Hans Walter ; Shields, Joseph C. ; Knecht, Matthias ; Hogg, David W. ; Maoz, Dan ; Bovy, Jo. / The color variability of quasars. In: Astrophysical Journal. 2012 ; Vol. 744, No. 2.
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