Blazar Optical Variability in the Palomar-QUEST Survey

TL;DR

This study analyzes optical variability in a large sample of blazars from the Palomar-QUEST Survey, revealing diverse fluctuation behaviors and correlations with radio jet velocities, aiding future identification and understanding of blazar variability.

Contribution

First large-scale ensemble optical variability analysis of blazars using the Palomar-QUEST Survey, characterizing variability properties and their relation to radio jet dynamics.

Findings

35% of blazars vary by more than 0.4 magnitudes

Blazar variability amplitudes are larger than those of type I quasars

Optical variability correlates with radio jet velocities

Abstract

We study the ensemble optical variability of 276 FSRQs and 86 BL Lacs in the Palomar-QUEST Survey with the goal of searching for common fluctuation properties, examining the range of behavior across the sample, and characterizing the appearance of blazars in such a survey so that future work can more easily identify such objects. The survey, which covers 15,000 square degrees multiple times over 3.5 years, allows for the first ensemble blazar study of this scale. Variability amplitude distributions are shown for the FSRQ and BL Lac samples for numerous time lags, and also studied through structure function analyses. Individual blazars show a wide range of variability amplitudes, timescales, and duty cycles. Of the best sampled objects, 35% are seen to vary by more than 0.4 magnitudes; for these, the fraction of measurements contributing to the high amplitude variability ranges constantly from about 5% to 80%. Blazar variability has some similarities to that of type I quasars but includes larger amplitude fluctuations on all timescales. FSRQ variability amplitudes are particularly similar to those of QSOs on timescales of several months, suggesting significant contributions from the accretion disk to the variable flux at these timescales. Optical variability amplitudes are correlated with the maximum apparent velocities of the radio jet for the subset of FSRQs with MOJAVE VLBA measurements, implying that the optically variable flux's strength is typically related to that of the radio emission. We also study CRATES radio-selected FSRQ candidates, which show similar variability characteristics to known FSRQs; this suggests a high purity for the CRATES sample.