GCN Circular 9415
Sheila McBreen (UCD/MPE) reports on behalf of the Fermi GBM Team: "At 08:27:58.35 UT on 16 May 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090516 (trigger 264155280 / 090516353). which was also detected by the Swift-BAT (Rowlinson et al. 2009, GCN 9374). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 20 degrees. The GBM light curve consists of about five overlapping pulses from T0-50 s to T+120 s. There is continued weak emission until about T0+300 s (8-1000 keV). Due to a large change in the spacecraft pointing during this long burst, a time averaged spectrum could not be fit. Instead three spectral intervals from -50 to 20 sec, 20 to 60 sec and 60 to 120 seconds were selected. The first interval was well fit by a power law function with an exponential high energy cutoff. The power law index is -1.51 ( +/-0.11 ) and the cutoff energy, parameterized as Epeak, is 185.6 (+98.4/-42.5) keV. The second and third intervals are adequately fit by a Band function. The parameters for interval two are alpha = -1.03 (+0.26/-0.31) , Epeak = 51.4 (+20.1, -11.4), beta= -2.1 ( +0.1/-0.2) and for the third interval, alpha = 0.30 (+1.30/ - 0.78), Epeak = 27.87 +/- 5.0), beta = -2.64 +/-0.4. The sum of the event fluence (8-1000 keV) in these time intervals is (2.3 +/- 0.5)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+28.6 s in the 8-1000 keV band is 5.3 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."