TITLE: GCN CIRCULAR NUMBER: 35259 SUBJECT: GRB 231203A: Fermi GBM Observation DATE: 23/12/04 22:31:12 GMT FROM: rachel.hamburg@ijclab.in2p3.fr R. Hamburg (CNRS/IN2P3) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:01:30.77 UT on 03 December 2023, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 231203A (trigger 723279695/231203293), which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2023, GCN 35257). The Fermi Final Localization was reported in GCN 35252. The angle from the Fermi LAT boresight is 59 degrees. The GBM light curve consists of multiple peaks with a duration (T90) of about 37 s (50-300 keV). The time-averaged spectrum from T0-1.1 to T0+28.6 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.92 +/- 0.05 and the cutoff energy, parameterized as Epeak, is 687 +/- 114 keV. The spectrum is also well fit by a Band function with Epeak = 543 +/- 108, alpha = -0.86 +/- 0.07, and beta = -2.10 +/- 0.30. The event fluence (10-1000 keV) in this time interval is (9.7 +/- 0.4)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.45 s in the 10-1000 keV band is 4.5 +/- 0.2 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/35259. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...