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Extreme gamma-ray outburst during the current Crab Nebula flare

ATel #3284; E. Hays (NASA/GSFC), R. Buehler (SLAC/KIPAC), F. D'Ammando (INAF-IASF Palermo, CIFS) on behalf of the Fermi Large Area Telescope Collaboration
on 15 Apr 2011; 14:18 UT
Credential Certification: Elizabeth Hays (elizabeth.a.hays@nasa.gov)

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

Referred to by ATel #: 3286, 4239, 4855

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, previously reported a new gamma-ray flare from the direction of the Crab Nebula beginning on the 9th of April (ATel #3276). The increased emission was afterwards confirmed by the AGILE satellite (ATel #3282).The Crab Nebula is currently also being monitored by Chandra, which observed a bright knot east of the pulsar (ATel #3283), similar to previous observations in the September 2010 flare.

Preliminary LAT analysis indicates that the gamma-ray emission (E >100 MeV) from the direction of the Crab continues to increase, reaching a peak flux of (12.1 +/-0.6) x10^-6 ph/cm2/sec (statistical errors only) on April 14th. This is the highest gamma-ray flux on daily scales which has been observed from this source. Preliminary analysis indicates flux variation on shorter time scales, reaching flux values of >15 x10^-6 ph/cm2/sec in 12-hour time periods. The average flux from the Crab is (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.

Fermi has interrupted all-sky scanning mode starting at 2011-04-12 16:47 UTC to observe the Crab Nebula and is expected to remain in this observing mode until the 19th of April, unless the flare fades before this date. 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.