TITLE: GCN CIRCULAR NUMBER: 45010 SUBJECT: GRB 260618B: Fermi GBM Observation DATE: 26/06/19 17:39:30 GMT FROM: Peter Veres at University of Alabama in Huntsville <veresp@gmail.com> P. Veres (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 16:55:04.71 UT on 18 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260618B (trigger 803494509/260618705), which was also detected by Fermi/LAT (Gupta et al., GCN 44983) and SVOM/VT (Li et al., GCN 45001). The Fermi GBM on-ground location is consistent with the LAT and the SVOM/VT position. The angle from the Fermi LAT boresight is 16 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 20 s (50-300 keV). The time-averaged spectrum from T0 to T0+10 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.42 +/- 0.01 and the cutoff energy, parameterized as Epeak, is 1030 +/- 20 keV. The event fluence (10-1000 keV) in this time interval is (9.4 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+0.96 s in the 10-1000 keV band is 4.3 +/- 0.2 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 1000 +/- 20 keV, alpha = -0.41 +/- 0.02 and beta = -3.2 +/- 0.2. 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/45010. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...