Detection of Periodic Variability in Simulated QSO Light Curves

Westman, David

We have studied a method for testing a large sample of QSOs light curves for periodic variations, which might indicate the presence of an eclipsing binary QSO system. Recently the author participated in research which employed the Lomb-Scargle periodigram (Lomb 1976, Scargle 1982, Horne and Baliunas, 1985) to test ~9000 spectroscopically confirmed QSOs from SDSS Stripe 82 (S82) for periodic variability (McLeod, et al., 2010 in press). The results of this work did not detect any examples of periodic variation in the QSOs studied that could not be attributed to spurious reasons. The false-alarm probability threshold (FAP) for this work, at which the strongest peak in a periodigram could be distinguished from white noise, was set at the 0.05 level.

Subsequently, the author employed the same algorithm to test 1x10^6 simulated QSO light curves for periodic variations. These light curves were based on the damped random walk model studied in McLeod et al., 2010. These light curves covered a large variety of possible combinations of black hole mass, luminosity, and redshift. They were sampled according to cadences established for the Large Synoptic Survey Telescope (LSST) so that the possible QSO population as observed by this telescope could be studied. After the light curve data were created and sampled, they were processed by Lomb-Scargle software to determine the effectiveness of this method and the actual fraction of the light curves that could not be eliminated by the false-alarm test. The light curves that were not eliminated by the false-alarm test were studied to determine the causes for this failure, and to develop a method for sorting a truly periodic variation pattern from those that could arise from spurious causes.

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