GCN Circular 8917
E. Bissaldi (MPE) reports on behalf of the Fermi GBM Team: "At 07:25:57.00 UT on 27 February 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090227 (trigger 257412359 / 090227310). The on-ground calculated location, using the GBM trigger data, is RA = 3.2, DEC = -43.1 (J2000 degrees, equivalent to 00h 13m, -43d 06'), with an uncertainty of 1.2 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 21 degrees. This burst was also independently detected by INTEGRAL SPI-ACS. The GBM light curve shows one main FRED-like pulse with substructure. Emission continues to at least 80 seconds. T90 (8-1000 keV) is about 50 s and T50 (8-1000 keV) is about 20 s. The time-averaged spectrum from T0 to T0+16.3 s is adequately fit by a power law function with an exponential high energy cutoff. The power law index is -0.91 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 1355 +/- 259 keV (chi squared 748 for 729 d.o.f.). The event fluence (8-1000 keV) in this time interval is (9.0 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.9 s in the 8-1000 keV band is 4.57 +/- 0.13 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 748 for 728 d.o.f.) with Epeak = 1357 +/- 284 keV, alpha = -0.92 +/- 0.06 and beta = -3.6 +/- 2.9. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."