GCN Circular 27558
B. Mailyan (Institute for Basic Science, South Korea) and R. Hamburg (UAH) report on behalf of the Fermi GBM Team: "At 09:08:40.71 UT on 12 April 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 200412B (trigger 608375325 / 200412381), which was also detected by the Fermi LAT (Longo et al. 2020, GCN 27557) and observed to have a candidate optical afterglow by MASTER (GCN 27555 & GCN 27556). The GBM on-ground location is consistent with the LAT position. The angle from the Fermi LAT boresight at the GBM trigger time is 59 degrees. The GBM light curve shows a multi-peaked structure with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0+3.1s to T0+21.5 s is best fit by a Band function with Epeak = 257 +/- 4 keV, alpha = -0.54 +/- 0.01, and beta = -2.24 +/- 0.02. The event fluence (10-1000 keV) in this time interval is (8.00 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+9.1 s in the 10-1000 keV band is 127.5 +/- 0.7 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"