TITLE: GCN CIRCULAR NUMBER: 10210 SUBJECT: GRB 091128: Fermi GBM detection DATE: 09/11/30 14:03:42 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 06:50:34.64 UT on 28 November 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 091128 (trigger 281083836 / 091128285). The on-ground calculated location, using the GBM trigger data, is RA = 127.7, DEC = 1.7 (J2000 degrees, equivalent to 08h 30m, 01d 42'), with an uncertainty of 1.4 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 96 degrees. This burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve shows one structured peak with a duration (T90) of 97.0 +/- 1.6 s (8-1000 keV). The time-averaged spectrum from T0-24.832 s to T0+71.425 s is best fit by a power law function with an exponential high energy cutoff. The power law index is -0.99 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 178.8 +/- 5.6 keV (C-stat 495 for 238 d.o.f.). The event fluence (8-1000 keV) in this time interval is (37.6 +/- 0.7)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+6.912 s in the 8-1000 keV band is 9.3 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well (C-stat 495 for 237 d.o.f.) with Epeak= 177.4 +/- 6.4 keV, alpha = -0.99 +/- 0.02 and beta = -3.9 +/- 1.5. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."