TITLE: GCN CIRCULAR NUMBER: 9904 SUBJECT: GRB 090910: Fermi GBM detection DATE: 09/09/11 19:32:46 GMT FROM: Vandiver Chaplin at UAH/Fermi-GBM V.Chaplin (UAH) reports on behalf of the Fermi GBM Team: "At 19:29:48.81 UT on 10 SEP 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090910 (trigger 274303790 / 090910812). The on-ground calculated location, using the GBM trigger data, is RA = 296.2, DEC = 72.3 (J2000 degrees, equivalent to 19h 44m, 72 d 18'), with an uncertainty of 1.0 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT boresight is 107 degrees. The on-board GBM Flight Software localization for this event, as reported in the GCN notice, was consistent with a position near the Earth's limb. Furthermore, the trigger occurred as the spacecraft was at a high magnetic latitude. The resulting autonomous classification for the event was "Distant Particles", which is erroneous. The GBM light curve consists of three distinct pulses close in time from T0-5s to about T0+45s, with a smaller pulse visible in several detectors at about T0+70s. The duration (T90) of this event is approximately 62s (8-1000 keV). The time-averaged spectrum from T0-7.2 s to T0+44 s is best fit by a Band function with Epeak = 274.8 +/- 56.1 keV, alpha = -0.9 +/- 0.1, and beta = -2.0 +/- 0.2 (chi squared 397.41 for 360 d.o.f.). The event fluence (8-1000 keV) in this time interval is (9.2 +/- 0.7)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2 s in the 8-1000 keV band is 2.3 +/- 0.6 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."