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Fermi LAT detection of X8.2 solar flare of September 10, 2017

ATel #10735; Francesco Longo (University of Trieste and INFN, Trieste), Melissa Pesce-Rollins (INFN-Pisa, Pisa) on behalf of the Fermi LAT collaboration
on 11 Sep 2017; 21:52 UT
Credential Certification: Francesco Longo (francesco.longo@ts.infn.it)

Subjects: Gamma Ray, >GeV, The Sun

On 10 September 2017 the Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, observed bright gamma-ray emission from the X8.2 class solar flare that erupted from the Solar AR 12673. In a preliminary analysis, using the dedicated Solar Flare event selection P8R2_TRANSIENT015S that is less affected by pile-up effects, the Sun was detected in gamma rays with a flux (E > 100 MeV) of (2.4+/-0.2) x10^-3 ph cm^-2 s^-1 over a 10 ks period starting on Sep 10, 15:46:59 UT, a factor of more than 5000 higher than the Quiet Sun gamma-ray flux (Abdo et al. 2011, ApJ, 734, 116) and a factor of 50 brighter than the X9.3 solar flare of Sep 6 (ATEL#10720). This flare is also associated with the second Ground Level Enhancement (GLE) of the current solar cycle (GLE #72). 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.