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

ATel #4855; Roopesh Ojha (NASA/GSFC), Elizabeth Hays (NASA/GSFC), Rolf Buehler (DESY Zeuthen) and Michael Dutka (CUA) on behalf of the Fermi Large Area Telescope Collaboration
on 4 Mar 2013; 19:15 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

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The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a significant increase in the gamma-ray activity from a source positionally consistent with the Crab Nebula on March 3, 2013.

Preliminary LAT analysis indicates that the daily-averaged gamma-ray emission (E >100 MeV) from the direction of the Crab nebula was (8.3 +/- 0.7) x 10^-6 ph cm^-2 s^-1 (statistical errors only) on March 3. This is a factor of 3 greater than the average flux of (2.75 +/- 0.10) x 10^-6 ph cm^-2 s^-1 reported in the second Fermi LAT catalog (2FGL, Nolan et al. 2012, ApJS, 199, 31). All fluxes given are the sums of the pulsar and nebular emission. This is the highest daily averaged flux measured since the April 2011 flare (ATel #3276, ATel #3282, ATel #3284, ATel #3286) and the first flare of the Crab Nebula since July 2012 (ATel #4239). Preliminary analysis for the beginning of March 4 indicates that the gamma-ray emission remains high.

Fermi has interrupted all-sky scanning mode on March 4 starting at 15:30 UTC to observe the Crab Nebula and is expected to remain in this observing mode for up to 300 ks, depending on when the flare fades. This source is one of the "LAT Monitored Sources" and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available (link:http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/ ). We strongly encourage further multifrequency observations of that region. For this source the Fermi LAT contact person is Rolf Buehler (rolf.buehler@desy.de).

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.