TITLE: GCN CIRCULAR NUMBER: 9035 SUBJECT: GRB 090323: Fermi GBM Spectral Analysis DATE: 09/03/25 03:11:27 GMT FROM: Alexander van der Horst at NASA/MSFC A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of the Fermi GBM team: "We have performed spectral analysis of the GBM data for GRB 090323 (GCN 9021). The analysis was restricted to the first ~70 seconds of GRB emission, because after that time the Fermi Observatory executed a maneuver following this bright GRB, which caused rapid, significant changes in the source angles of the various detectors and in the background behaviour. The spectrum from T0-2.0 s to T0+71.7 s is best fit by a power-law function with a high-energy exponential cutoff. The power-law index is -0.89 +/- 0.03, and the cutoff energy, parameterized as Epeak, is 697 +/- 51 keV (chi squared 379.4 for 359 d.o.f.). At a redshift of 3.57 (GCN 9028), the Epeak in the GRB rest frame, Epeak_rest, is 3.19 +/- 0.23 MeV. The event fluence (8-1000 keV) in this time interval is (1.00 +/- 0.01)E-4 erg/cm^2. The 1-sec peak photon flux measured starting from T0+65.5 s in the 8-1000 keV band is 12.3 +/- 0.4 ph/s/cm^2. This time interval consists of two main emission peaks, from T0-2.0 s to T0+33.8 s and from T0+33.8 s to T0+71.7 s. Both of these shorter intervals are also best fit by a power-law function with a high-energy exponential cutoff. For the first interval the power-law index is -1.00 +/- 0.03, Epeak is 1173 +/- 175 keV, Epeak_rest is 5.36 +/- 0.80 MeV, and the fluence (8-1000 keV) is (3.68 +/- 0.06)E-5. For the second interval the power-law index is -0.83 +/- 0.03, Epeak is 574 +/- 34 keV, Epeak_rest is 2.62 +/- 0.16 MeV, and the fluence (8-1000 keV) is (6.35 +/- 0.09)E-5. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."