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Fermi LAT detection of a new enhanced gamma-ray emission from the Crab Nebula region

ATel #3276; R. Buehler (SLAC/KIPAC), F. D'Ammando (INAF-IASF Palermo, CIFS), A. Cannon (University College Dublin, NASA/GSFC) on behalf of the Fermi Large Area Telescope Collaboration
on 12 Apr 2011; 16:21 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Rolf Buehler (buehler@slac.stanford.edu)

Subjects: Gamma Ray, >GeV, Neutron Star, Transient, Pulsar

Referred to by ATel #: 3279, 3282, 3283, 3284, 3286, 4239, 4855

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a renewed increase of the gamma-ray activity from a source positionally consistent with the Crab Nebula in the period April 9-11, 2011.

Preliminary LAT analysis indicates that the gamma-ray emission (E >100 MeV) observed at the location of the Crab Nebula started to increase on 9 April with a flux of (4.7 +/- 0.6) x10^-6 ph/cm2/sec (only statistical errors are given), and a peak in the period between 2011-04-11 05:59:58 UT and 2011-04-11 23:44:56 UT of (5.7 +/- 0.7) x10^-6 ph/cm2/sec, corresponding to an increase of a factor of 2 with respect to the average flux from the direction of the Crab nebula of (2.9 +/- 0.1) x10^-6 ph/cm2/sec, estimated for the entire Fermi operation period. All given fluxes are the sum of the pulsar and nebula emission.

A gamma-ray flux increase from the direction of the Crab Nebula was reported previously by the AGILE and LAT collaborations in September 2010 (ATel #2855 and ATel #2861). We strongly encourage further multifrequency observations of that region. For this source the Fermi LAT contact person is Rolf Buehler (buehler@stanford.edu).

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.