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Fermi LAT strong detection of blazar AO 0235+164 during outburst at Optical-to-Radio Wavelengths

ATEL # 1744; Stephane Corbel (University Paris Diderot & CEA Saclay) and Luis C. Reyes (KICP - University of Chicago) on behalf of the Fermi Large Area Telescope Collaboration
on 26 Sep 2008; 2:18 UT
Password Certification: Gino Tosti (

Subjects: Gamma Ray, >GeV, AGN, Quasars
Referred to by ATEL #: 1746

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST) (launched June 11, 2008), has observed an upward trend in gamma-ray flux for a source positionally consistent with blazar AO 0235+16 since Sept 1st, 2008. The source was recently reported in a very high state in optical to radio bands by Villata et al (ATEL #1724) and Balonek and Lam (ATEL #1735).

Preliminary analysis indicates that the source has brightened to a gamma-ray flux (E>100MeV) comparable to the pre-defined LAT flaring source reporting threshold of 2x10-6 photons cm-2 s-1. This well known BL Lac object (redshift=0.940; Cohen et al. 1987, ApJ, 18, 577) was detected by EGRET as 3EG J0237+1635 (Hartman et al., 1999, ApJS, 123, 79), at a much lower flux than the current one (EGRET average flux: 2.6x10-7 photons cm-2 s-1; peak flux 6.5x10-7 photons cm-2 s-1).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. AO 0235+16 is one of the "LAT Monitored Sources" (, and consequently, a preliminary, uncalibrated estimation of the gamma-ray flux observed by Fermi LAT is publicly available ( In consideration of the ongoing activity of this source we strongly encourage multiwavelength observations. For this source the Fermi LAT contact person is Luis C. Reyes (e-mail:

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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