We quantify quasar color-variability using an unprecedented variability
database - ugriz photometry of 9093 quasars from 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 decayed 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 disc.
%0 Generic
%1 Schmidt2011
%A Schmidt, Kasper B.
%A Rix, Hans-Walter
%A Shields, Joseph C.
%A Knecht, Matthias
%A Hogg, David W.
%A Maoz, Dan
%A Bovy, Jo
%D 2011
%K quasar variability
%T The Color Variability of Quasars
%U http://arxiv.org/abs/1109.6653
%X We quantify quasar color-variability using an unprecedented variability
database - ugriz photometry of 9093 quasars from 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 decayed 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 disc.
@misc{Schmidt2011,
abstract = { We quantify quasar color-variability using an unprecedented variability
database - ugriz photometry of 9093 quasars from 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 decayed 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 disc.
},
added-at = {2011-10-03T06:40:29.000+0200},
author = {Schmidt, Kasper B. and Rix, Hans-Walter and Shields, Joseph C. and Knecht, Matthias and Hogg, David W. and Maoz, Dan and Bovy, Jo},
biburl = {https://www.bibsonomy.org/bibtex/261ba7b2a789ebbed1225d8af62cabf32/miki},
description = {[1109.6653] The Color Variability of Quasars},
interhash = {ae9e43a9e0f4993bd3b8b5d96b651c82},
intrahash = {61ba7b2a789ebbed1225d8af62cabf32},
keywords = {quasar variability},
note = {cite arxiv:1109.6653Comment: Accepted for publication in ApJ, 17 pages, 14 figures},
timestamp = {2011-10-03T06:40:29.000+0200},
title = {The Color Variability of Quasars},
url = {http://arxiv.org/abs/1109.6653},
year = 2011
}