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

ATel #5485; Sara Buson (INFN/Univ. of Padova), Rolf Buehler (DESY Zeuthen), Elizabeth Hays (NASA/GSFC) on behalf of the Fermi Large Area Telescope Collaboration
on 18 Oct 2013; 17:44 UT
Credential Certification: Sara Buson (buson@pd.infn.it)

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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 2013 October 17.

Preliminary LAT analysis indicates that the daily-averaged gamma-ray emission (E >100 MeV) from the direction of the Crab Nebula was (9.7+/-0.7) x 10^-6 ph cm^-2 s^-1 (statistical errors only) on October 17. This is about a factor of 3.5 greater than the average gamma-ray flux of (2.75+/-0.02) 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. The daily averaged flux measured on October 17 is similar to the peak flux value observed during the 2013 March flare (Mayer et al. 2013, ApJL 775, 37; ATel #4855; ATel #4867; ATel #4869; ATel #4878).

Fermi will interrupt all-sky scanning mode and maximize the exposure toward the Crab Nebula for at least 300 ks. 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.