TITLE: GCN CIRCULAR NUMBER: 9933 SUBJECT: GRB 090926: Fermi GBM detection DATE: 09/09/26 14:27:11 GMT FROM: Elisabetta Bissaldi at MPE Elisabetta Bissaldi (MPE) reports on behalf of the Fermi GBM Team: "At 04:20:26.99 UT on 26 September 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090926 (trigger 275631628 / 090926181). The on-ground calculated location, using the GBM trigger data, is RA = 354.5, DEC = -64.2 (J2000 degrees, equivalent to 23h 38m, -64d 12'), with an uncertainty of 1.0 degree (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 48 degrees. Moreover, this burst was bright enough to result in a Fermi spacecraft repointing maneuver. The burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve consists of single pulse with a duration (T90) of 20 +/- 2 s (8-1000 keV). The time-averaged spectrum from T0 to T0+21 s is best fit by a Band function with Epeak = 314 (+/- 4) keV, alpha = -0.75 (+/-0.01) and beta = -2.59 (+0.04/-0.05) (C-stat 1136 for 478 d.o.f.). The event fluence (8-1000 keV) in this time interval is (1.45 +/- 0.04)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3 s in the 8-1000 keV band is 80.8 +/- 0.4 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."