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Fermi-LAT confirmation of enhanced gamma-ray activity from the Crab nebula

ATel #9588; C. C. Cheung (NRL), on behalf of the Fermi Large Area Telescope Collaboration
on 3 Oct 2016; 18:43 UT
Credential Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)

Subjects: Gamma Ray, >GeV, Transient, Pulsar

Referred to by ATel #: 9617

Preliminary LAT analysis confirms the recent enhanced gamma-ray activity from the Crab nebula detected by AGILE (ATel #9586). The daily-averaged gamma-ray fluxes (E>100 MeV) from the direction of the Crab Nebula were (4.8 +/- 0.5) x 10^-6 ph cm^-2 s^-1 (Sep 30), (3.3 +/- 0.4) x 10^-6 ph cm^-2 s^-1 (Oct 1), and (4.5 +/- 0.5) x 10^-6 ph cm^-2 s^-1 (Oct 2). These are up to a factor of ~1.8 greater than the average gamma-ray flux of (2.71 +/- 0.02) x 10^-6 ph cm^-2 s^-1 reported in the third Fermi-LAT source catalog (Acero et al. 2015, ApJS, 218, 23). All fluxes given are the sums of the pulsar and nebular emission, and with statistical uncertainties only. These are the highest fluxes observed for the Crab since 2016 January (ATel #8519).

Fermi will interrupt the currently planned observations and maximize the coverage toward the Crab nebula for at least 350 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 this 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.