GCN Circular 9688
Arne Rau (MPE) reports on behalf of the Fermi GBM Team: "At 06:38:08.28 UT on 20 July 20009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090720 (trigger 269764690 / 090720276). The on-ground calculated location, using the GBM trigger data, is RA = 199.5, DEC = -16.4 (J2000 degrees, equivalent to 13 h 18 m, -16 d 24 '), with an uncertainty of 5.0 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 113 degrees. This burst was also independently detected (but not triggered) by INTEGRAL SPI-ACS. The GBM light curve shows a single peak with a duration (T90) of about 7.0 s (8-1000 keV). The time-averaged spectrum from T0-1.856 s to T0+5.312 s is best fit by a power law function with an exponential high energy cutoff. The power law index is -0.75 +/- 0.10 and the cutoff energy, parameterized as Epeak, is 117.50 +/- 7.12 keV (chi squared 507 for 507 d.o.f.). The event fluence (8-1000 keV) in this time interval is (2.9 +/- 0.1)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+0.002 s in the 8-1000 keV band is 10.9 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."