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

Abstract

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 findmore » 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.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [2]
  1. Stanford Univ., CA (United States)
  2. Univ. of California, Berkeley, CA (United States)
  3. NASA/Marshall Space Flight Center, Huntsville, AL (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1560651
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 880; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies: active; galaxies: jets; relativistic processes

Citation Formats

Liodakis, Ioannis, Romani, Roger W., Filippenko, Alexei V., Kocevski, Daniel, and Zheng, WeiKang. Probing Blazar Emission Processes with Optical/Gamma-Ray Flare Correlations. United States: N. p., 2019. Web. doi:10.3847/1538-4357/ab26b7.
Liodakis, Ioannis, Romani, Roger W., Filippenko, Alexei V., Kocevski, Daniel, & Zheng, WeiKang. Probing Blazar Emission Processes with Optical/Gamma-Ray Flare Correlations. United States. doi:10.3847/1538-4357/ab26b7.
Liodakis, Ioannis, Romani, Roger W., Filippenko, Alexei V., Kocevski, Daniel, and Zheng, WeiKang. Mon . "Probing Blazar Emission Processes with Optical/Gamma-Ray Flare Correlations". United States. doi:10.3847/1538-4357/ab26b7.
@article{osti_1560651,
title = {Probing Blazar Emission Processes with Optical/Gamma-Ray Flare Correlations},
author = {Liodakis, Ioannis and Romani, Roger W. and Filippenko, Alexei V. and Kocevski, Daniel and Zheng, WeiKang},
abstractNote = {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.},
doi = {10.3847/1538-4357/ab26b7},
journal = {The Astrophysical Journal (Online)},
number = 1,
volume = 880,
place = {United States},
year = {2019},
month = {7}
}

Journal Article:
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