TITLE: GCN CIRCULAR NUMBER: 18130 SUBJECT: GRB 150811B: Fermi GBM detection DATE: 15/08/12 02:59:05 GMT FROM: Peter Jenke at MSFC P. Jenke (UAH) reports on behalf of the Fermi GBM Team: "At 20:22:13.75 UT on August 11 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150811B (trigger 461017337/150811849). The GBM on-ground location, using the Fermi GBM trigger data, is RA = 188.0, Dec = -13.5 (J2000 degrees, equivalent to 12h 32m 00s, -13d 30'), with an uncertainty of 8.7 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 of the burst direction to the Fermi LAT boresight is 108 degrees. The GBM light curve consists of a single peak with a duration (T90) of about 0.6 s (50-300 keV). The time-averaged spectrum from T0-0.13 s to T0+0.64 s is adequately fit by a Band function with Epeak = 1300 +/- 100 keV, Alpha =-0.23 +/- 0.07 and Beta = -3.0 +/- 0.2. The event fluence (10-1000 keV) in this time interval is (1.6 +/- 0.1)E-07 erg/cm^2. The 64 ms peak photon flux measured starting from T0-0.13 s in the 10-1000 keV band is 8.6 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."