SIMILARITY OF THE OPTICAL-INFRARED AND γ-RAY TIME VARIABILITY OF<i>FERMI</i>BLAZARS

Abstract

We present the time variability properties of a sample of six blazars, AO\n0235+164, 3C 273, 3C 279, PKS 1510-089, PKS 2155-304, and 3C 454.3, at\noptical-IR as well as gamma-ray energies. These observations were carried out\nas a part of the Yale/SMARTS program during 2008-2010 that has followed the\nvariations in emission of the bright Fermi-LAT-monitored blazars in the\nsouthern sky with closely-spaced observations at BVRJK bands. We find the\noptical/IR time variability properties of these blazars to be remarkably\nsimilar to those at the gamma-ray energies. The power spectral density (PSD)\nfunctions of the R-band variability of all six blazars are fit well by simple\npower-law functions with negative slope such that there is higher amplitude\nvariability on longer timescales. No clear break is identified in the PSD of\nany of the sources. The average slope of the PSD of R-band variability of these\nblazars is similar to what was found by the Fermi team for the gamma-ray\nvariability of a larger sample of bright blazars. This is consistent with\nleptonic models where the optical-IR and gamma-ray emission is generated by the\nsame population of electrons through synchrotron and inverse-Compton processes,\nrespectively. The prominent flares present in the optical-IR as well as the\ngamma-ray light curves of these blazars are predominantly symmetric, i.e., have\nsimilar rise and decay timescales, indicating that the long-term variability is\ndominated by the crossing time of radiation or a disturbance through the\nemission region rather than by the acceleration or energy-loss timescales of\nthe radiating electrons. In the blazar 3C 454.3, which has the highest-quality\nlight curves, the location of a large gamma-ray outburst during 2009 December\nis consistent with being in the jet at ~18 pc from the central engine. This\nposes strong constraints on the models of high energy emission in the jets of\nblazars.\n