TITLE: GCN CIRCULAR NUMBER: 41517 SUBJECT: GRB 250823A: Fermi GBM Observation DATE: 25/08/24 02:09:14 GMT FROM: Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu> Jacob Smith (UAH), B. Mailyan (Florida Tech) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: At 20:10:10.67 UT on 23 August 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250823A (trigger 777672615/250823840), which was also detected by Swift BAT (M. H. Siegel et al. 2025, GCN 41511), and optical follow-up was first reported by Liverpool Telescope (B. P. Gompertz et al. 2025, GCN 41512). The Fermi GBM on-ground location is consistent with the Swift BAT position. The angle from the Fermi LAT boresight is 72 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 13 s (50-300 keV). The time-averaged spectrum from T0-6.1 to T0+10.2 s is best fit by a simple power law function with index -1.67 +/- 0.05. A power law function with an exponential high-energy cutoff fits equally well with power law index = -1.44 +/- 0.17 and Epeak = 206.5 +/- 95.8. The event fluence (10-1000 keV) in this time interval is (1.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1.1 s in the 10-1000 keV band is 1.8 +/- 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/41517. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...