TITLE: GCN CIRCULAR NUMBER: 9429 SUBJECT: GRB 090520D: Fermi GBM detection DATE: 09/05/28 13:45:04 GMT FROM: Narayana Bhat at U Alabama/Huntsville/GBM P. N. Bhat (UAH) reports on behalf of the Fermi GBM Team: "At 21:01:37.14 UT on 20 May 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090520D (trigger 264546099 / 090520876). The on-ground calculated location, using the GBM trigger data, is RA = 131.3, DEC = -18.0 (J2000 degrees, equivalent to 08 h 45.2 m, -18 d 0'), with an uncertainty of 4.3 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 66 degrees. The GBM light curve consists of single pulse with a duration (T90) of about 12 s (8-1000 keV). The time-averaged spectrum from T0-5.12 s to T0+13.3 s is adequately fit by a power law function with an exponential high energy cutoff. The power law index is -1.03 +/- 0.22 and the cutoff energy, parameterized as Epeak, is 47.4 +/- 4.1 keV (chi squared 354 for 363 d.o.f.). The event fluence (8-1000 keV) in this time interval is (4.0 +/- 0.9)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+2.0 s in the 8-1000 keV band is 4.1 +/- 1.0 ph/s/cm^2. A Band function fits the spectrum equally well (chi squared 353.8 for 362 d.o.f.) with Epeak= 46.3 +/- 5.3 keV, alpha = -0.99 +/- 0.28 and beta = -3.25 +/- 1.23. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."