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Fermi LAT detection of 3C 273 in flaring state

ATel #1707; M. Marelli (INAF/IASF Milano) on behalf of the Fermi Large Area Telescope Collaboration
on 8 Sep 2008; 22:12 UT
Credential Certification: Gino Tosti (tosti@pg.infn.it)

Subjects: Gamma Ray, >GeV, AGN, Quasar

Referred to by ATel #: 2168, 2200

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST, launched June 11, 2008), has observed high flux from a source positionally consistent with 3C 273 (J2000, R.A. :12:29:06.6997, Dec:+02:03:08.598 Johnston et al. 1995, AJ, 110, 880) starting on 5 September 2008.

Preliminary analysis indicates that the source has brightened to a high state with a gamma-ray flux (E>100MeV) near the pre-defined LAT flaring source reporting threshold of 2x10-6 photons cm-2 s-1.

This well known radio source, classified as a flat spectrum radio quasar (FSRQ), has a redshift of 0.158 (see e.g., Strauss et al., 1992, ApJS, 83, 29). It was first detected as a high energy gamma-ray source by COS-B (Swanenburg et al. 1978, Nature, 275, 298) and was observed by EGRET as 3EG J1229+0210 (Hartman et al. 1999, ApJS, 123, 79) at a level of flux lower than the current one (EGRET average flux: 1.75x10-7 photons cm-2 s-1; peak flux: 1.27x10-6 photons cm-2 s-1;Nandikotkur et al. 2007, ApJ, 657, 706).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source we strongly encourage multiwavelength observations, although the position of 3C273 near the Sun will make many observations difficult at this time.

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.