GCN Circular 9792
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 04:10:42.59 UT on 13 August 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090813 (trigger 271829444 / 090813174), which was also detected by the SWIFT-BAT (Cummings et al. 2009, GCN 9781) and Konus/Wind (Golenetskii et al., 2009, GCN Circular 9787). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 35.3 degrees. This burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve consists of two separate pulses with a duration (T90) of about 9 s (8-1000 keV). The time-averaged spectrum from T0-0.256 s to T0+8.960 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -1.43 +/- 0.08 an the cutoff energy, parameterized as Epeak, is 161 +/- 26 keV (chi squared 495 for 480 d.o.f.). The event fluence (8-1000 keV) in this time interval is (3.5 +/- 0.2)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.512 s in the 8-1000 keV band is 14.4 +/- 0.5 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 492 for 479 d.o.f.) with Epeak= 95 +/- 30 keV, alpha = -1.25 +/- 0.18 and beta = -2.0 +/- 0.1. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."