TITLE: GCN CIRCULAR NUMBER: 43851 SUBJECT: GRB 260226A: Fermi GBM observation DATE: 26/02/26 16:21:05 GMT FROM: Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi@ba.infn.it> E. Bissaldi (Politecnico and INFN Bari), O.J. Roberts (Uni. of Galway, Ireland), P. Veres (UAH) and A. von Kienlin (MPE) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 10:39:05 UT on 26 February 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260226A (trigger 793795080/260226443), which was also detected by Fermi-LAT (Depalo et al. 2026, GCN 43844 and 43850) and AstroSat CZTI (Harsha et al. 2026, GCN 43846). The Fermi GBM on-ground location (GCN 43840) is consistent with the Fermi-LAT position. The angle from the Fermi LAT boresight is 26 degrees. The GBM light curve consists of a very bright and structured emission episode with a duration (T90) of about 82 s (50-300 keV). The time-averaged spectrum from T0 to T0+81 s is best fit by a Band function with Epeak = 723 +/- 8 keV, alpha = -0.95 +/- 0.01, and beta = -2.47 +/- 0.02. The event fluence (10-1000 keV) in this time interval is (4.54 +/- 0.01)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+19.3 s in the 10-1000 keV band is 166 +/- 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/43851. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...