TITLE: GCN CIRCULAR NUMBER: 17561 SUBJECT: GRB 150309A: Fermi GBM detection DATE: 15/03/10 15:13:46 GMT FROM: Oliver Roberts at UCD/Fermi O.J Roberts (UCD) and M. Stanbro (UAH) report on behalf of the Fermi GBM Team: "At 22:59:50.66 UT on the 9th of March 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150309A (trigger 447634793/150309958), the second episode of which was also detected by Swift (Cummings et al. 2015, GCN 17553). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 60 degrees. The Swift trigger is observed in the GBM light curve at T0+200 s as a very soft, weak event with a duration of about 60 s. The immediate light curve at the GBM trigger time consists of a bright, main peak of unresolved emission episodes, with a duration (T90) of about 52 s (50-300 keV). The time-averaged spectrum from T0+0.0 s to T0+52.6 s is best fit by a Band function with Epeak= 165 +/- 4 keV, alpha = -0.59 +/- 0.02 and beta = -2.59 +/- 0.10. The event fluence (10-1000 keV) in this time interval is (3.9 +/- 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+17.5 s in the 10-1000 keV band is 15.2 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."