GCN Circular 14473
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 07:47:06.42 UT on 27 April 2013, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 130427A (trigger 388741629/130427324) which was also detected by the Swift/BAT and Fermi/LAT (Maselli et al. 2013, GCN 14448 and S. Zhu et al., GCN 14471) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 48 degrees. Based on hard and intense emission in a GBM BGO detector, GBM initiated an Autonomous Report Request. This request caused Fermi to reorient towards this GRB (GBM flight location). The GBM light curve consists of a bright structured peak followed at ~T0+120 s by a FRED-like pulse. The overall duration (T90) is about 138s s (50-300 keV). Owing to the brightness of the burst, systematic effects are very large and no single model gives an adequate fit in this preliminary analysis. A Band function fit in the interval from T0+0.002 s to T0+18.432 s yields the following parameters Epeak = 830 +/- 5 keV, alpha = -0.789 +/- 0.003, and beta = -3.06 +/- 0.02. The event fluence (10-1000 keV) in this time interval is (1.975 +/- 0.003)E-03 erg/cm^2. The 1.024 sec peak photon flux measured starting from T0+7.48808 s in the 8-1000 keV band is 1052 +/- 2 ph/s/cm^2, making this the most intense and fluent GRB detected by Fermi GBM. Further analysis is being performed"