GCN Circular 24701
M. Axelsson (KTH and Stockholm Univ.), M. Arimoto (Kanazawa Univ.), D. Kocevski (NASA/MSFC) and F. Longo (Univ. and INFN Trieste) report on behalf of the Fermi-LAT team: On May 31, 2019, Fermi-LAT detected high-energy emission from GRB 190531B, which was also detected by Fermi-GBM (trigger 581026217 / 190531840; GCN 24695). The best LAT on-ground location is found to be RA, Dec 24.37, -41.97 (degrees, J2000) with an error radius of 0.11 deg (90% containment, statistical error only). This was 25 deg from the LAT boresight at the time of the GBM trigger: T0 = 20:10:12.14 UT. The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is spatially and temporally correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-700 s after the GBM trigger is 8.9e-6 ph/cm2/s. The highest-energy photon in this interval is a 7.0 GeV event observed at T0+325s. The estimated photon index above 100 MeV is -2.1 +/- 0.2. The Fermi-LAT point of contact for this burst is Francesco Longo (Francesco.Longo@ts.infn.it<mailto: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.