TITLE: GCN CIRCULAR NUMBER: 18756 SUBJECT: GRB 151229A: Fermi GBM observation DATE: 15/12/29 17:07:57 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 06:50:27.95 UT on 29 December 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 151229A (trigger 473064631 / 151229285 ), which was also detected by the Swift/BAT (Kocevski et al. 2015, GCN 18745) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 53.4 degrees. The GBM light curve consists of a single peak with a duration (T90) of about 3.5 s (50-300 keV). The time-averaged spectrum from T0-0.256: s to T0+1.280 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.19 (+0.10/-0.09) and the cutoff energy, parameterized as Epeak, is 97.1 (+10.3/-8.3) keV The event fluence (10-1000 keV) in this time interval is (9.4 +/- 0.5)E-07 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0-0.128 s in the 10-1000 keV band is 11.0 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."