Fermi LAT and INTEGRAL detection of increasing high-energy activity of blazar 3C279

ATel #2154; G. Iafrate (INAF/OA Trieste), F. Longo (INFN Trieste), Werner Collmar (MPE); on behalf of the Fermi Large Area Telescope Collaboration
on 7 Aug 2009; 22:50 UT
Credential Certification: Francesco Longo (francesco.longo@ts.infn.it)

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The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed, by weekly data averages, an active state during the last 5 weeks with a rising gamma-ray flux during the last 3 weeks in the gamma-ray flux from a source positionally consistent with the blazar 3C279 (J2000, R.A.: 12h56m11.1665s, Dec: 05d47m21.523s). Preliminary analysis indicates that the source was in a high state with a gamma-ray flux (E>100 MeV) of (1.38 +/- 0.12) x 10^-6 ph cm^-2 s^-1 (statistical uncertainty only) during the week 2009 Jul 29 - Aug 04, a factor of 2 higher than the steady source level during the past months.

This gamma-ray activity is accompanied by a high state in hard X-rays. INTEGRAL, observing the blazar between Jul 31 (01:02 UT) and Aug 02, 2009 (09:20 UT) for 116 ksec effective on-source exposure, detected the blazar with IBIS/ISGRI significantly (6.6 sigma) in the energy band 20 to 200 keV. Quick-look analysis by the ISDC/INTEGRAL team yields a flux of 1.6 mCrab (20-40 keV) and 5.8 mCrab (40-80 keV). A hard spectral shape of power-law index (1.3 ± 0.3) is indicated, the hardest one measured by INTEGRAL yet.

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).

A similar rise in activity was reported by the LAT team in December, 2008 (ATEL #1864).

The Fermi-LAT contact people for this source are Greg Madejski (madejski@slac.stanford.edu) and Werner Collmar (wec@mpe.mpg.de). 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.

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.