TITLE: GCN CIRCULAR NUMBER: 42513 SUBJECT: GRB 251026B: Fermi GBM Observation DATE: 25/10/29 14:40:22 GMT FROM: Marianna Dafčíková at Masaryk University <500025@mail.muni.cz> M. Dafcikova (MUNI) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 07:18:53.33 UT on 26 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251026B (trigger 783155938/251026305). The angle from the Fermi LAT boresight is 19 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 6 s (50-300 keV). The time-averaged spectrum from T0-1.3 to T0+3.7 s is best fit by a simple power law function with index -1.38 +/- 0.04. The event fluence (10-1000 keV) in this time interval is (7.2 +/- 0.7)E-07 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.32 s in the 10-1000 keV band is 1.6 +/- 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/42513. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...