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Fermi LAT detections of increasing gamma ray activity of blazar 3C 279

ATEL # 1864; S. Ciprini (Univ. Perugia & INFN Perugia), S. Chaty (CNRS-Univ. Paris Diderot & CEA Saclay); on behalf of the Fermi Large Area Telescope Collaboration
on 6 Dec 2008; 18:43 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Stefano Ciprini (

Subjects: Gamma Ray, >GeV, AGN, Quasars

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST, launched June 11, 2008), has observed a weekly-averaged continuous and increasing trend in the gamma-ray flux from the blazar 3C 279 (J2000, R.A. :12h56m11.1665s, Dec:-05d47m21.523s) for the last six weeks. Preliminary analysis indicates that the source is continuing this high state with a gamma-ray flux (E>100MeV) now in excess of 1.5 x 10-6 photons cm-2 s-1.

This well known radio source, classified as a flat spectrum radio quasar (FSRQ), has a redshift of 0.536 (Marziani et al. ApJS, 1996, 104, 37). It is also a well known gamma-ray blazar: it was detected by EGRET as 3EG J1255-0549 (Hartman et al. 1999, ApJS, 123, 79) and more recently, as a source of very-high-energy emission (E> 100 GeV) by the MAGIC experiment (Albert et al. 2008, Science, 320, 5884).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of 3C 279 will continue. In consideration of this long-term and increasing trend, of the current high state and flux level, of the known behavior during the past EGRET era (an intensification like this was followed by the biggest flare ever seen, Wehrle et al. 1998, ApJ, 497, 178 ), and finally that the source is being far enough from the Sun position to allow multiwaveband observations and monitoring by ground-based and space borne observatories, we strongly encourage multiwavelength observations.

This source is one of the "LAT Publicly Monitored Sources" and, consequently, a preliminary estimate of the daily and weekly gamma-ray flux will be made publicly available by the Fermi Science Support Center. For this source the Fermi LAT contact persons are Greg Madejski ( and Werner Collmar (

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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