TITLE: GCN CIRCULAR NUMBER: 9427 SUBJECT: GRB 090520B: Fermi GBM detection DATE: 09/05/28 13:19:11 GMT FROM: Narayana Bhat at U Alabama/Huntsville/GBM P. N. Bhat (UAH) report on behalf of the Fermi GBM Team: "At 19:57:53.98 UT on 20 May 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090520B (trigger 264542275 / 090520832). [which was the second GRB trigger of the day while the first was detected by the Swift-BAT (Cummings et al. 2008, GCN 9417)] The on-ground calculated location, using the GBM trigger data, is RA = 332.0, DEC = 43.2 (J2000 degrees, equivalent to 22 h 08 m, 43 d 12'), with an uncertainty of 12 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 10 degrees. The GBM light curve consists of a single pulse with a duration (T90) of about 1.5 s (8-1000 keV). The time-averaged spectrum from T0-0.384 s to T0+0.256 s is adequately fit by a simple power law function with index -1.4 +/- 0.1 (chi squared 98 for 122 d.o.f.). The event fluence (8-1000 keV) in this time interval is (4.5 +/- 0.2)E-7 erg/cm^2. The 1-sec peak photon flux measured starting from T0 s in the 8-1000 keV band is 4.1 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."