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Fermi LAT detection of increasing gamma-ray flux from B2 1520+31

ATEL # 3050; David Sanchez (LLR/Ecole Polytechnique/CNRS/IN2P3) on behalf of the Fermi Large Area Telescope Collaboration
on 22 Nov 2010; 20:23 UT
Password Certification: Berrie Giebels (

Subjects: Gamma Ray, >GeV, AGN

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has detected enhancement of the gamma-ray flux of a source positionally consistent with the Flat Spectrum Radio Quasar B2 1520+31 (RA: 15 22 09.99 , Dec: +31 44 14.4 , J2000, A. J. Beasley et al. 2002, ApJS, 41, 13 ) with a redshift of z=1.487 (D. Sowards-Emmerd et al. 2005, ApJ, 626, 95).

Preliminary analysis indicates that the source flux was (1.80.3)x10-6 photons cm-2 s-1 (E>100 MeV, where errors are statistical only) on November 18. The source was still at a high activity state on November 19, 20 and 21, with a decreasing flux of (1.3 0.3)x10-6 photons cm-2 s-1. This flux is a factor 100 greater than reported in the first year LAT Catalog (1FGL J1522.1+3143, Abdo et al. 2010, ApJS 188, 405). In consideration of the ongoing activity of this source, we strongly encourage multiwavelength observations. The Fermi-LAT already detected a flaring episode on April 2009 (ATel #2026) during which the source reached a lower daily flux of (1.00.3)x10-6 photons cm-2s-1

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. The Fermi LAT contact people for this source is Dario Gasparrini (

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.

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