TITLE: GCN CIRCULAR NUMBER: 8111 SUBJECT: GLAST Burst Monitor detection of a GRB: 080816B DATE: 08/08/21 22:31:00 GMT FROM: Rob Preece at UAH R. D. Preece (UAHuntsville) and A.J. van der Horst (NASA/ORAU) report on behalf of the GLAST Burst Monitor Team: "At 23:44:01 UT on 16 August, 2008, the GLAST Burst Monitor (GBM) triggered and located GRB 080816B (trigger 240623035 / 080816.989). The on-ground calculated location, using the GBM trigger data, is RA = 288.5, Dec = -6.5 (J2000 degrees) (equivalent to J2000 19h 14m, -06d 30'), with an uncertainty of 5.2 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 Large Area Telescope (LAT) boresight is 70 degrees. This GRB was about 5 s long with 2 peaks, showing structure on the 64 ms time scale. The time-averaged spectrum from T-3.584 to T+1.536 s, in the energy range 6 keV to 3500 keV, is best fit with a power law times exponential cutoff. The power law index is -0.37 +/- 0.17 and the cutoff energy, parameterized as Epeak, is 1230 +/- 230 keV. We note that this is a hard event. The average photon flux is 1.38 +/- 0.08 ph/s-cm^2 in the energy interval 25 - 1000 keV. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."