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The Second Catalog of Flaring Gamma-Ray Sources from the Fermi All-sky Variability Analysis
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Number of Authors: 127
2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 846, no 1, 34Article in journal (Refereed) Published
Abstract [en]

We present the second catalog of flaring gamma-ray sources (2FAV) detected with the Fermi All-sky Variability Analysis (FAVA), a tool that blindly searches for transients over the entire sky observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. With respect to the first FAVA catalog, this catalog benefits from a larger data set, the latest LAT data release (Pass 8), as well as from an improved analysis that includes likelihood techniques for a more precise localization of the transients. Applying this analysis to the first 7.4 years of Fermi observations, and in two separate energy bands 0.1-0.8 GeV and 0.8-300 GeV, a total of 4547 flares were detected with significance greater than 6s (before trials), on the timescale of one week. Through spatial clustering of these flares, 518 variable gamma-ray sources were identified. Based on positional coincidence, likely counterparts have been found for 441 sources, mostly among the blazar class of active galactic nuclei. For 77 2FAV sources, no likely gamma-ray counterpart has been found. For each source in the catalog, we provide the time, location, and spectrum of each flaring episode. Studying the spectra of the flares, we observe a harder-when-brighter behavior for flares associated with blazars, with the exception of BL Lac flares detected in the low-energy band. The photon indexes of the flares are never significantly smaller than 1.5. For a leptonic model, and under the assumption of isotropy, this limit suggests that the spectrum of freshly accelerated electrons is never harder than p similar to 2.

Place, publisher, year, edition, pages
2017. Vol. 846, no 1, 34
Keyword [en]
astroparticle physics, catalogs, galaxies: active, gamma rays: general, techniques: photometric
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-147015DOI: 10.3847/1538-4357/aa8092ISI: 000408687300011OAI: oai:DiVA.org:su-147015DiVA: diva2:1145437
Available from: 2017-09-29 Created: 2017-09-29 Last updated: 2017-09-29Bibliographically approved

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Conrad, Jan
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Department of PhysicsThe Oskar Klein Centre for Cosmo Particle Physics (OKC)
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