GCN Circular 8922
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 07:33:37.98 UT on 01 March 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090301B (trigger 257585619 / 090301315 ). The on-ground calculated location, using the GBM trigger data, is RA = 350.3, DEC = 9.0 (J2000 degrees, equivalent to 23h 21m, 09d 00'), with an uncertainty of 4.2 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 Fermi LAT boresight is 56 degrees. The GBM light curve shows a single peak lasting about 5 s superimposed on a lower-level continuum. The burst duration (T90) is about 28 s (8-1000 keV) The time-averaged spectrum from T0-1.536 s to T0+3.584 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -1.03 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 546 +/- 133 keV (chi squared 703.17 for 731 d.o.f.). The event fluence (8-1000 keV) in this time interval is (2.69 +/- 0.13)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.536 s in the 8-1000 keV band is 4.4 +/- 0.1 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 700.28 for 730 d.o.f.) with Epeak= 427 +/- 147 keV, alpha = -0.98 +/- 0.12 and beta = -1.93 +/- 0.24. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."