Correlated Infrared-Gamma-ray Variability in Bright, Well-Monitored Blazars 2008-2017


Yoshida K, Bailyn C, Cruz B, Urry CM, Coppi P, Vasilopoulous G, Petropoulou M. Correlated Infrared-Gamma-ray Variability in Bright, Well-Monitored Blazars 2008-2017. In: Vol. 233. ; 2019. pp. 454.10.

Date Presented:



We present cross correlations of the J-band SMARTS light curves and Fermi gamma-ray light curves for 8 bright blazars that have been monitored extensively on sub-weekly time scales over the past decade. Because of the uneven temporal sampling, we use the Discrete Correlation Function (DCF) and we create an empirical boot-strapping method to assess the significance of the DCF amplitude for each blazar. Our results are perhaps surprising. Early on in the Fermi mission, the flaring blazar 3C454.3 showed zero lag between optical and gamma-ray or infrared and gamma-ray fluxes, which Bonning et al. (2012) suggested was consistent with the gamma rays being produced by inverse Compton scattering of ambient photons by synchrotron-emitting electrons. However, of the 8 blazars we examine, only one - 3C454.3 - shows a significant peak at zero lag. The other seven show no significant peak at zero lag. Some blazars show broad peaks at lags of 10s of days, at or just below 3 sigma significance. In addition, analyses of time periods of a year or two only, for a given blazar, show strong changes from one epoch to the next. These results complicate our understanding of blazar emission mechanisms. Possible physical explanations are discussed.