TITLE: GCN CIRCULAR NUMBER: 44972 SUBJECT: GRB 260617A: Fermi GBM Detection DATE: 26/06/18 05:18:48 GMT FROM: Matt Godwin <msg0028@uah.edu> Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 21:36:43.68 UT on 17 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260617A (trigger 803425008/260617900). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 224.34, Dec = -12.61 (J2000 degrees, equivalent to J2000 15h 47m, -16d 43'), with a statistical uncertainty of 7.08 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 99 degrees. The GBM light curve consists of a short, bright burst with a duration (T90) of about 0.14 s (50-300 keV). The time-averaged spectrum from T0-0.08 to T0+0.259 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.56 +/- 0.04 and the cutoff energy, parameterized as Epeak, is 700 +/- 40 keV. The event fluence (10-1000 keV) in this time interval is (7.4 +/- 0.5)E-07 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.0 s in the 10-1000 keV band is 21 +/- 1 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/44972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...