TITLE: GCN CIRCULAR NUMBER: 9366 SUBJECT: GRB 090509: Fermi GBM observation DATE: 09/05/15 15:33:09 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) and Sheila McBreen (UCD/MPE) report on behalf of the Fermi GBM Team: "At 05:10:05.72 UT on 09 May 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090509 (trigger 263538607 / 090509215) which was also detected by the SWIFT-BAT (Grupe et al. 2008, GCN 9325; Krimm et al., GCN 9349). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 75 degrees. The GBM light curve consists of two widely separated multi-peaked emission periods with a duration (T90) of about 295 s (8-1000 keV). The time-averaged spectrum of the first emission complex from T0-3.072 to T0+24.576 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -0.90 +/- 0.16 and the cutoff energy, parameterized as Epeak, is 343 +/- 93 keV (chi squared 375 for 360 d.o.f.). The time-averaged spectrum of the second emission complex from T0+239.619 s to T0+288.772 s is best fit by a simple power law function with index -1.55 +/- 0.07 (chi squared 328 for 361 d.o.f.). The summed event fluence (8-1000 keV) of both time intervals is (8.4 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+18.432 s in the 8-1000 keV band is 3.1 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."