GCN Circular 43046
Subject
GRB 251208B: Fermi GBM Observation
Event
Date
2025-12-09T11:51:58Z (a day ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
Via
email
A. von Kienlin (MPE) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 10:17:17.29 UT on 08 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251208B (trigger 786881842/251208429).
which was also detected by Fermi-LAT (E. Bissaldi et al. 2025, GCN 43034)
and Swift/BAT-GUANO (GCN #43033). The Fermi GBM on-ground location was reported
by the Fermi-GBM team in GCN 43028 and is consistent with the Fermi-LAT
and Swift/BAT positions.
The GBM light curve shows a structured emission episode with a duration (T90)
of about 62.5 s (50-300 keV). The time-averaged spectrum
from T0-4.1 to T0+61.4 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.67 +/- 0.08 and the cutoff energy,
parameterized as Epeak, is 250 +/- 20 keV.
The event fluence (10-1000 keV) in this time interval is
(9.5 +/- 0.5)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+55 s in the 10-1000 keV band is 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/"