TITLE: GCN CIRCULAR NUMBER: 40621 SUBJECT: GRB 250601A: Fermi GBM Observation DATE: 25/06/03 15:42:16 GMT FROM: Vidushi Sharma at NASA GSFC/UMBC vidushi.sharma@nasa.gov
V. Sharma (NASA-GSFC/UMBC) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 17:29:35 UT on 1 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250601A (trigger 770491780 / 250601729). which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2025, GCN 40600) and Swift/XRT (K.L. Page et al. 2025, GCN 40604). The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.
The angle from the Fermi LAT boresight is 24 degrees.
The GBM light curve consists of main emission episode with a duration (T90) of about 3 s (50-300 keV). The time-averaged spectrum from T0-0.5 to T0+2.4 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.58 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 873 +/- 142 keV.
The event fluence (10-1000 keV) in this time interval is (2.7 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+1 s in the 10-1000 keV band is 4.9 +/- 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/"
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