Gamma-Ray Emission from Two Blazars Behind the Galactic Plane: B2013+370 & B2023+336

TL;DR

This study confirms that two low-galactic-latitude gamma-ray sources are blazars, using Fermi-LAT data, radio and X-ray observations, revealing their variability and typical spectral energy distribution, supporting their extragalactic nature.

Contribution

It provides the first multiwavelength confirmation that these two gamma-ray sources are blazars, clarifying their nature and origin.

Findings

Gamma-ray emission is spatially compatible with the blazars.

Both sources show significant variability in gamma-ray and radio bands.

Spectral energy distribution exhibits a typical two-component blazar structure.

Abstract

B2013+370 and B2023+336 are two blazars at low-galactic latitude that were previously proposed to be the counterparts for the EGRET unidentified sources, 3EG J2016+3657 and 3EG J2027+3429. Gamma-ray emission associated with the EGRET sources has been detected by the Fermi Gamma-ray Space Telescope, and the two sources, 1FGL J2015.7+3708 and 1FGL J2027.6+3335, have been classified as unidentified in the 1-year catalog. This analysis of the Fermi-LAT data collected during 31 months reveals that the 1FGL sources are spatially compatible with the blazars, and are significantly variable, supporting the hypothesis of extragalactic origin for the gamma-ray emission. The gamma-ray light curves are compared with 15 GHz radio light curves from the 40-m telescope at the Owens Valley Radio Observatory (OVRO). Simultaneous variability is seen in both bands for the two blazar candidates. The study is completed with the X-ray analysis of 1FGL J2015.7+3708 using Swift observations that were triggered in August 2010 by a Fermi-detected flare. The resulting spectral energy distribution shows a two-component structure typical of blazars. We also identify a second source in the field of view of 1FGL J2027.6+3335 with similar characteristics to the known LAT pulsars. This study gives solid evidence favoring blazar counterparts for these two unidentified EGRET and Fermi sources, supporting the hypothesis that a number of unidentified gamma-ray sources at low galactic latitudes are indeed of extragalactic origin.