TITLE: GCN CIRCULAR NUMBER: 39688 SUBJECT: GRB 250302A: Fermi GBM Observation DATE: 25/03/12 17:18:02 GMT FROM: Marianna Dafčíková at Masaryk University 500025@mail.muni.cz
M. Dafcikova (MUNI) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 13:46:32.99 UT on 02 March 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250302A (trigger 762615997/250302574). which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2025, GCN 39675). The Fermi GBM on-ground location is consistent with the Swift/BAT position.
The angle from the Fermi LAT boresight is 67 degrees.
The GBM light curve consists of multiple peaks with a duration (T90) of about 56 s (50-300 keV). The time-averaged spectrum from T0-3.6 to T0+71.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.49 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 394 +/- 135 keV.
The event fluence (10-1000 keV) in this time interval is (8.8 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 2.5 +/- 0.2 ph/s/cm^2.
A Band function fits the spectrum equally well with Epeak = 324 +/- 194 keV, alpha = -1.48 +/- 0.09 and beta = -2.0 +/- 0.3.
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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