TITLE: GCN CIRCULAR NUMBER: 30058 SUBJECT: Fermi GBM observation of a bright burst from magneta DATE: 21/05/20 13:08:44 GMT FROM: Rachel Dunwoody at UCD S. Lesage (UAH) reports on behalf of the Fermi GBM Team: "At 19:22:03.94 UT on 19 May 2021, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located a bright, SGR-like burst from the direction of the magnetar SGR J1745−2900 (trigger 643144928/210519807). The GBM on-ground location is consistent with the known position of the SGR. The burst has a duration (T90) of about 0.3 s (10-300 keV). It is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -0.6 +/- 0.5 and the cutoff energy, parameterized as Epeak, is 37 +/- 4 keV. The event fluence (10-300 keV) from T0-0.256s to T0+0.064s is (1.4 +/- 0.1)E-07 erg/cm^2. The average photon flux in the 10-300 keV band during this period is 9.5 +/- 0.7 ph/s/cm^2. The spectral analysis results presented above are preliminary. For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"