TITLE: GCN CIRCULAR NUMBER: 45044 SUBJECT: GRB 260618A: Fermi GBM Observation DATE: 26/06/25 13:02:58 GMT FROM: Christian Malacaria at INAF-OAR <cmalacaria.astro@gmail.com> C. Malacaria (INAF-OAR) and R. Sonawane (IISER, TVM) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 06:45:34.28 UT on 18 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260618A (trigger 803457939/260618282). Final Real-time localization was reported in GCN 44973. A possible afterglow is detected by EP (Yang et al., GCN 44978, Jiang et al., GCN 44991). The GBM light curve consists of a variable emission episode with a duration (T90) of about 140 s (50-300 keV). The time-averaged spectrum from T0-17 to T0+150 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.4 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 43 +/- 2 keV. The event fluence (10-1000 keV) in this time interval is (5.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+25 s in the 10-1000 keV band is 2.7 +/- 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/45044. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...