TITLE: GCN CIRCULAR NUMBER: 35632 SUBJECT: GRB 240123B: Fermi GBM Observation DATE: 24/01/25 19:45:45 GMT FROM: Lorenzo Scotton at UAH <lscottongcn@outlook.com> L. Scotton (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 17:48:03.22 UT on 23 January 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 240123B (trigger 727724888/240123742). which was also detected by Swift/BAT-GUANO (Ronchini et al. 2024, GCN 35629). The Fermi GBM Final Real-time Localization was reported in GCN 35608. The angle from the Fermi LAT boresight is 51 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 12 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+11.5 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.6 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 250 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (2.6 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.9 s in the 10-1000 keV band is 2.4 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 130 +/- 30 keV, alpha = 0.1 +/- 0.4 and beta = -1.9 +/- 0.1. 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/35632. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...