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

ATel #11412; Janeth Valverde (LLR/Ecole Polytechnique), Roopesh Ojha (NASA/GSFC/UMBC) and Rolf Buehler (DESY) on behalf of the Fermi Large Area Telescope Collaboration
on 12 Mar 2018; 22:24 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

Subjects: Gamma Ray, >GeV, Pulsar

Referred to by ATel #: 11415

Preliminary Fermi LAT analysis reveals enhanced gamma-ray activity from the direction of the Crab Nebula. The daily-averaged gamma-ray flux (E>100 MeV) on 11 March 2018 from the direction of the Crab Nebula was (4.9 +/- 0.5) x 10^-6 ph cm^-2 s^-1. This is a factor of ~2 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). The flux values in the last two 6-hour periods of 11 March 2018 were ~ (6.0 +/- 1.0) x 10^-6 ph cm^-2 s^-1. All fluxes given are the sums of the pulsar and nebular emission, and with statistical uncertainties only. These are the highest gamma-ray fluxes observed for the Crab since October 2016 (ATel 9588).

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.