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

ATel #5971; D. Gasparrini (ASDC/INAF), R. Buehler (DESY) on behalf of the Fermi LAT Collaboration
on 11 Mar 2014; 20:40 UT
Credential Certification: Dario Gasparrini (dario.gasparrini@asdc.asi.it)

Subjects: Gamma Ray, >GeV, Pulsar

Referred to by ATel #: 5976, 6401

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 2014 March 10.

Preliminary LAT analysis on March 10 indicates that the daily-averaged gamma-ray emission (E >100 MeV) from the direction of the Crab Nebula was 5.7 +- 0.5 x 10^-6 ph cm^-2 s^-1 (statistical errors only) on March 10. This is about a factor of 2 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. This is the highest flux observed since 2013 October (ATel #5485). It has been increasing since 2014 March 7 and has not yet peaked.

Fermi will interrupt the currently planned observations 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 (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.