Probing Blazar Emission Processes with Optical/Gamma-Ray Flare Correlations

Liodakis, Ioannis; Romani, Roger W.; Filippenko, Alexei V.; Kocevski, Daniel; Zheng, WeiKang

doi:10.3847/1538-4357/ab26b7

Title: Probing Blazar Emission Processes with Optical/Gamma-Ray Flare Correlations

Journal Article · Mon Jul 22 00:00:00 EDT 2019 · The Astrophysical Journal (Online)

DOI:https://doi.org/10.3847/1538-4357/ab26b7· OSTI ID:1560651

^[1];

^[2]; Kocevski, Daniel ^[3];

^[2]

Stanford Univ., CA (United States)
Univ. of California, Berkeley, CA (United States)
NASA/Marshall Space Flight Center, Huntsville, AL (United States)

We report that even with several thousand Fermi-Large Area Telescope (LAT) blazar detections, the γ-ray emission mechanism is poorly understood. We explore correlated optical/γ-ray flux variations for 178 Fermi-LAT blazars regularly monitored by the Katzman Automatic Imaging Telescope, the Small and Moderate Aperture Research Telescope System, and the Steward Observatory. Out of the 178 sources, 121 show a measurable (>1σ) discrete correlation function peak. Using the derived time lags and Bayesian block light-curve decompositions, we measure the fraction of common and orphan flares between the two bands. After accounting for sampling and sensitivity limitations we quantify for the first time the true orphan flare rates of optical and γ-ray flares: 54.5% of optical and 20% of γ-ray flares are orphan events. Both the intraband temporal relation and the small orphan γ-ray flare fraction point toward leptonic processes as the likely mechanisms for the high-energy emission. Motivated to discriminate between synchrotron self-Compton (SSC) and external-Compton dominance in individual sources, we use the flux–flux variations to determine the slope m of the log f _opt–log f _γ dependence. The slope distribution suggests a bimodal population with high and intermediate synchrotron peak objects showing larger m than low synchrotron peak objects. We find that m is naturally decreased through pollution from the orphan (typically optical) flares and develop a method to statistically recover, given the sources' measured orphan flare rate, the intrinsic m. Finally, while source classes show composite behavior, the majority of BL Lac objects favor m = 2, indicating an SSC origin for the γ-rays. No preference for either m is found in flat spectrum radio quasars.

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Research Organization:: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: AC02-76SF00515

OSTI ID:: 1560651

Journal Information:: The Astrophysical Journal (Online), Vol. 880, Issue 1; ISSN 1538-4357

Publisher:: Institute of Physics (IOP)Copyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 27 works

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