GCN Circular 42965
Subject
GRB 251201B: Fermi GBM Observation
Event
Date
2025-12-02T20:57:29Z (2 days ago)
From
Eva Palafox at INAOE <eva.palafox@gmail.com>
Via
Web form
Eva Palafox (INAOE) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 16:26:24.22 UT on 01 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251201B (trigger 786299189/251201685),
which was also detected by Swift BAT (M. J. Moss et al. 2025, GCN 42924), and Swift XRT (J.P. Osborne et al. 2025, GCN 42927).
The Fermi GBM on-ground location (GCN 42923) is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 119 degrees.
The GBM light curve consists of a single emission episode with a duration (T90)
of about 91 s (50-300 keV).
The time-averaged spectrum from T0-22.5 to T0+105.5 s is best fit by
a simple power law function with index -1.83 +/- 0.04.
A power law function with an exponential high-energy cutoff fits equally well with power
law index = -1.71 +/- 0.08 and Epeak = 269.8 +/- 166.0.
The event fluence (10-1000 keV) in this time interval is
(1.2 +/- 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.7 s in the 10-1000 keV band is 4 +/- 0.3 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/"