TITLE: GCN CIRCULAR NUMBER: 38714 SUBJECT: GRB 241228B: Fermi GBM Observation DATE: 24/12/29 21:37:56 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 04:13:05.39 UT on 28 December 2024, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 241228B (trigger 757051990/241228176), which was also detected by Swift/BAT-NITRATES (J. DeLaunay et al. 2024, GCN 38700). The Fermi GBM on-ground location is consistent with the Swift/BAT-NITRATES position. Follow-up observations report the detection of the potential afterglow (Kumar et al. GCN 38684 and GCN 38691; An et al. GCN 38687; Ortega-Casas et al. GCN 38692; Mohan et al. GCN 38694; Ghosh et al. GCN 38702, Burrows et al. GCN 38713) at a redshift z = 2.674 (An et al. GCN 38704). The angle from the Fermi LAT boresight is 49 degrees. The GBM light curve consists of two emission episodes, with a duration (T90) of about 19.5 s (50-300 keV). The time-averaged spectrum from T0-0.7 to T0+23.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.86 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 440 +/- 10 keV. The event fluence (10-1000 keV) in this time interval is (4.66 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+4.2 s in the 10-1000 keV band is 15.1 +/- 0.3 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/38714. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...