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Fermi LAT detection of X-class solar flares of September 6, 2017

ATel #10720; F. Longo (University and INFN, Trieste), N. Omodei (Stanford University/KIPAC), S. Digel (Stanford University/KIPAC) on behalf of the Fermi Large Area Telescope Collaboration
on 7 Sep 2017; 21:17 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Nicola Omodei (nicola.omodei@gmail.com)

Subjects: Gamma Ray, >GeV, The Sun

Referred to by ATel #: 10735

On September 6, 2017 the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed gamma-ray emission from the X-class solar flares emitted by the Solar AR 12673 and detected also by Fermi/GBM. In the preliminary analysis, using the Solar Flare dedicated event selection P8R2_TRANSIENT015S less affected by pile-up effects, the Sun was detected in gamma rays for the first flare with a flux (E > 100 MeV) of (1.7+/-0.2) x10^-5 ph cm^-2 s^-1 over a 3.3 ks period starting on Sep 6, 08:20:08 UT, when it entered in the LAT field of view. The Sun was also detected starting at Sep 6, 11:46:04 UT for approximately 12 hours, with a maximum flux of (4.4+/-0.7) x10^-5 ph cm^-2 s^-1 a factor of 30 and 100 higher with respect to the Quiet Sun gamma-ray flux (Abdo et al. 2011, The Astrophysical Journal, Volume 734, Number 2). Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of the Sun will continue. For these Solar flares the Fermi-LAT contact person is Francesco Longo: francesco.longo@ts.infn.it. 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.