TITLE: GCN CIRCULAR NUMBER: 40802 SUBJECT: GRB 250619B: Fermi GBM Observation DATE: 25/06/21 01:38:07 GMT FROM: Jacob Smith at Fermi-GBM Team jrs0118@uah.edu
Jacob Smith (UAH) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
At 23:36:17.17 UT on 19 June 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250619B (trigger 772068982/250619984). which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2025, GCN 40795). The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.
The angle from the Fermi LAT boresight is 48 degrees.
The GBM light curve consists of a double emission episode with a duration (T90) of about 29 s (50-300 keV). The time-averaged spectrum from T0-1 to T0+28.7 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.1 +/- 0.2 and the cutoff energy, parameterized as Epeak, is 67 +/- 9 keV. A Band function fits the spectrum equally well with Epeak = 57 +/- 13 keV, alpha = -1 +/- 0.4 and beta = -2.5 +/- 0.4.
The event fluence (10-1000 keV) in this time interval is (1.4 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.32 s in the 10-1000 keV band is 2.2 +/- 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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