GCN Circular 9895
A. Goldstein (UAH) reports on behalf of the Fermi GBM Team: "At 01:24:13.93 UT on 04 September 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090904B (trigger 273720255 / 090904058), which was also detected by the SWIFT-BAT (D'Elia et al. 2009, GCN 9881). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 113 degrees. The GBM light curve consists of three bright peaks with a duration (T90) of about 71 s (8-1000 keV). The time-averaged spectrum from T0-9.2 s to T0+65.5 s is well fit by a power law function with an exponential high energy cutoff. The power law index is 1.41 +/- 0.08 and the cutoff energy, parameterized as Epeak, is 149.30 +/- 22.10 keV (chi squared 243.6 for 238 d.o.f.). The event fluence (8-1000 keV) in this time interval is (2.44 +/- 0.15)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+21.5 s in the 8-1000 keV band is 9.8 +/- 0.7 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 239.0 for 237 d.o.f.) with Epeak= 106.30 +/- 24.60 keV, alpha = -1.26 +/- 0.15 and beta = -2.18 +/- 0.18. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."