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Fermi LAT detection of increasing gamma-ray activity of 3C 454.3

ATEL # 2534; Eric Wallace (University of Washington) and Yasuyuki T. Tanaka (ISAS/JAXA) on behalf of the Fermi Large Area Telescope Collaboration
on 6 Apr 2010; 0:22 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Yasuyuki T. Tanaka (

Subjects: Gamma Ray, >GeV, AGN, Quasars, Transients
Referred to by ATEL #: 2535

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has detected an increasing gamma-ray activity from the blazar 3C 454.3. Preliminary analysis indicates that the source on 3rd April, 2010, has reached a very high state with an average gamma-ray flux over the day of (12 +/- 1) ~ 10-6 photons cm-2 s-1 (E>100 MeV, statistical only). This flux level in the GeV range is comparable to that of the Vela pulsar, the brightest persistent source in the gamma-ray sky. A previous flare from 3C 454.3 reached the flux of (22 +/- 1) x 10-6 photons cm-2 s-1 (E>100 MeV, statistical only) on 2nd December, 2009 (ATel #2328). Although the current flare has not reached this level so far, the GeV flux is still increasing. A Fermi Target of Opportunity observation of 3C 454.3 started at 19:38 UT on 5th April 2010 and will continue for 2.5 days (200 ksec). This observation will maximize the exposure toward 3C 454.3 during this time. Multiwavelength follow-up is therefore strongly encouraged. This is the fourth time Fermi has reported enhanced activity from this source (Jul 2008, ATel #1628; Sep 2009, ATel #2200; Dec 2009, ATel #2328).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. The blazar 3C 454.3 is a "LAT Monitored Source" (, and consequently, a quick look estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available ( The Fermi LAT contact person is Greg Madejski (

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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