TITLE: GCN CIRCULAR NUMBER: 10095 SUBJECT: GRB 091020: Fermi GBM observation DATE: 09/10/28 14:27:17 GMT FROM: Vandiver Chaplin at UAH/Fermi-GBM V.Chaplin (UAH) reports on behalf of the Fermi GBM Team: "At 21:36:43.82 UT on 20 October 2009, the Fermi Gamma-Ray Burst Monitor triggered on GRB 091020 (trigger 277767405 / 091020900), which was also detected by the Swift-BAT (Racusin et al., GCN 10048). The angle from the Fermi LAT boresight of the Swift-XRT position (Beardmore et al., GCN 10050) is 118 degrees. The GBM light curve consists of a single pulse with a duration (T90) of about 37 s (8-1000 keV). The time-averaged spectrum from T0-7.7 s to T0+21 s is best fit by a Band function with Epeak = 47.9 +/- 7.1 keV, alpha = 0.2 +/- 0.4, and beta = -1.7 +/- .02. The event fluence (8-1000 keV) in this time interval is (1.0 +/- 0.2)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.5 s in the 8-1000 keV band is 7.4 +/- 0.5 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."