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Published February 20, 2012 | Published
Journal Article Open

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


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 Large Area Telescope (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. 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 2010 August 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.

Additional Information

© 2012 American Astronomical Society. Received 2011 November 8; accepted 2011 December 12; published 2012 February 2. This research is supported by the NASA grants NNX09AU14G and NNX10AP66G, and the US National Science Foundation grant Phys-0855627. W.M. acknowledges support from the US Department of State and the Comisiόn Nacional de Investigaciόn Científica y Tecnolόgica (CONICYT) in Chile for a Fulbright- CONICYT scholarship. The authors thank Diego Tescaro for providing an alternative code to evaluate the discrete correlation function and Vito Sguera for sharing the X-ray spectra of B2023+336. W.M. and J.R. thank Joseph Lazio for a helpful discussion about extreme scattering events. The OVRO 40 m monitoring program is supported in part by NASA grants NNX08AW31G and NNG06GG1G and NSF grant AST-0808050. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States; the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France; the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy; the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK), and Japan Aerospace Exploration Agency (JAXA) in Japan; and the K. A. Wallenberg Foundation, the Swedish Research Council, and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d' Études Spatiales in France.

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