TITLE: GCN CIRCULAR NUMBER: 42364 SUBJECT: GRB 251018A: Fermi GBM Observation DATE: 25/10/18 21:53:57 GMT FROM: Glowbug DEV <boyan.a.hristov@nasa.gov> B. Hristov (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team: "At 03:12:00.63 UT on 18 October 2025 , the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 251018A (trigger 782449925 / 251018133), which was also detected by the Swift/XRT (R. Gupta et al. 2025, GCN 42343) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 42 degrees. The GBM light curve consists of multiple peaks, with a duration (T90) of about 27.1 s (50-300 keV). The time-averaged spectrum from T0-6.1 s to T0+21.5 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.91 +/- 0.09 and the cutoff energy, parameterized as Epeak, is 715 +/- 162 keV. The event fluence (10-1000 keV) in this time interval is (6.8 +/- 0.3)E-6 erg/cm^2. The 1-sec peak photon flux measured starting from T0+3 s in the 10-1000 keV band 0.95 +/- 0.04 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/42364. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...