TITLE: GCN CIRCULAR NUMBER: 35519 SUBJECT: GRB 240109A: Fermi GBM Observation DATE: 24/01/11 20:28:52 GMT FROM: Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov> O.J. Roberts (USRA/NASA-MSFC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 04:01:35.21 UT on 09 January 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240109A (trigger 726465700/240109168). which was also detected by Swift-BAT (S. Dichiara et al. 2024, GCN 35501). The Fermi GBM on-ground Localization is consistent with the Swift-BAT position. The angle from the Fermi LAT boresight is 79 degrees using the Swift-BAT position. The GBM light curve consists of a single peak with a duration (T90) of about 0.26 s (50-300 keV). The time-averaged spectrum from T0-0.12 to T0+0.12 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.0 +/- 0.3 and the cutoff energy, parameterized as Epeak, is 305 +/- 179 keV. The event fluence (10-1000 keV) in this time interval is (1.6 +/- 0.4)E-07 erg/cm^2. The 0.064-sec peak photon flux measured starting from T0-0.064 s in the 10-1000 keV band is 6 +/- 1 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/35519. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...