TITLE: GCN CIRCULAR NUMBER: 18229 SUBJECT: GRB 150902A: Fermi GBM detection DATE: 15/09/03 09:32:09 GMT FROM: Oliver Roberts at UCD/Fermi O.J. Roberts (UCD) and G. Younes (GWU) report on behalf of the Fermi GBM team: "At 17:35:39 UT on September 2nd 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150902A (trigger 462908143/150902733), which was also detected by Fermi-LAT (Axelsson et al. 2015, GCN 18228). The trigger resulted in an Autonomous Repoint Request (ARR) by the GBM Flight Software due to the high peak flux of the GRB. This ARR was accepted and the spacecraft slewed to the GBM in-flight location. Both the GBM in-flight and on-ground locations are consistent with the LAT position. The GBM light curve consists of a series of unresolved pulses, with a duration of about 14 s (50-300 keV). The time-averaged spectrum from T0+3.0s to T0+17.0s is well fit by a Band function with Epeak = 351.40 +/- 5.61 keV, Alpha =-0.48 +/- 0.02 and Beta = -2.32 +/- 0.03. The event fluence (10-1000 keV) in this time interval is (8.221 +/- 0.043)E-05 erg/cm^2. The 1.024 s peak photon flux measured starting from T0+8.8s in the 10-1000 keV band is 61.9 +/- 0.5 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."