Physics
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21910903s&link_type=abstract
American Astronomical Society, AAS Meeting #219, #109.03
Physics
Scientific paper
Quasars vary intrinsically by 10% over timescales of year(s). This variability has the potential of becoming an extremely powerful tool for quasar identification in the near future due to present (the Panoramic Survey Telescope & Rapid Response System 1; Pan-STARRS1) and future (the Large Synoptic Survey Telescope; LSST) wide-area multi-epoch surveys. Describing the variability of more than 9000 quasars from SDSS Stripe 82, the largest variability sample of quasars to date, by a power-law structure function we have illustrated how samples of quasar candidates with completeness and purity well above 90% is straightforwardly obtained. Applying our variability selection algorithm to data without u-band photometry that is crucial in color selection, as is the case for Pan-STARRS1 data, shows that variability selection of quasars is still capable of selecting complete and pure quasar candidate samples. Variability selection of quasars out-performs the usual color selection at redshifts where quasars have the same colors as stars. We find that at z 2.7 variability selection of quasars is up to 10 times more effective than color selection. Not only does the intrinsic quasar variability aid in quasar selection, it also contains vital information about the quasar/AGN accretion disk physics, which still has to be fully understood. Through robust fitting, including outlier pruning, we determined the color variability of the 9000 Stripe 82 quasars, i.e., the change of quasar color as their brightness changes on year time-scales. We found a strong redshift dependence of this color variability and showed that it is caused by the quasar's emission lines. Furthermore, we found that the characteristic color variability of the individual quasars is substantially stronger than the change of mean quasar color with L/Ledd, implying that changes in the overall accretion rate cannot explain the observed color variability.
Rix Herbert
Schmidt Kasper B.
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