GCN Circular 43068
Subject
GRB 251209A: Fermi GBM observation
Event
Date
2025-12-10T22:23:56Z (2 days ago)
From
Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi@ba.infn.it>
Via
Web form
E. Bissaldi (Politecnico and INFN Bari)
reports on behalf of the Fermi GBM Team:
"At 13:24:03.99 UT on 9 December 2025, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 251209A (trigger 786979448 / 251209558).
The Fermi GBM Final Real-time Localization is reported in GCN 43048.
The angle from the Fermi LAT boresight at the GBM trigger time is 52 degrees.
The GBM light curve consists of several structured emission episodes
with a duration (T90) of about 57 s (50-300 keV).
The time-averaged spectrum from T0-4 s to T0+81 s is
best fit by a Band function with Epeak = 105 +/- 4 keV,
alpha = -1.63 +/- 0.01, and beta = -2.37 +/- 0.06.
The event fluence (10-1000 keV) in this time interval is
(6.89 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+49.7 s in the 10-1000 keV band
is 38.4 +/- 0.6 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/"