Date Presented:

2020/01/1

Abstract:

We present the results of cross-correlation analysis between the Fermi-LAT gamma-ray and SMARTS optical/infrared light curves of bright 8 blazars monitored in 2008-2017. For the temporal correlation analysis of unevenly sampled variability data, we use the Discrete Correlation Function (DCF), and created an empirical bootstrapping method to assess the significance of the DCF amplitude for each blazar. The DCFs between gamma-ray and optical/infrared light curves with one week binning time scale suggest that 6 of the 8 blazars show a significant peak at zero lag at or above 3 sigma level. That is consistent with the leptonic model in which optical/infrared photons are produced by synchrotron radiation of relativistic electrons and gamma rays are produced by inverse Compton scattering of ambient photons by the synchrotron-emitting electrons. However, the DCFs with one day binning time scale suggest that among 8 blazars, only one blazar — 3C 454.3 — still has a significant peak at zero lag. The other 7 blazars tend to show much smaller peaks than those with a weekly time bin. In addition, for a given blazar, strong changes of the DCFs from one epoch to the next are shown by the analyses of time periods of one or two years. These results complicate the simplest understanding of blazar emission mechanisms. We discuss possible physical explanations.

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