GCN Circular 43222
Subject
GRB 251222A: Fermi GBM Observation
Event
Date
2025-12-23T18:39:59Z (22 days ago)
From
eliza.neights@gmail.com
Via
Web form
Eliza Neights (GWU, NASA GSFC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 17:05:51.27 UT on 22 December 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251222A (trigger 788115956/251222712).
which was also detected by SVOM ECLAIRs, GRM, and MXT (H. Yang et al. 2025, GCN 43188),
SVOM VT (J. T. Palmerio et al. 2025, GCN 43189), NOT (J. An et al. 2025, GCN 43194),
Calapai Observatory (G. Calapai et al. 2025, GCN 43195), PRIME (J. Durbak et al. 2025, GCN 43197),
EP WXT (C.-L. Guo et al. 2025, GCN 43201), DFOT (A. Gupta et al. 2025, GCN 43207),
LCO (A. Saccardi et al. 2025, GCN 43208; I. Pérez-Fournon et al. 2025, GCN 43212),
GOTO (A. Kumar et al. 2025, GCN 43209), Swift XRT (A.P. Beardmore et al. 2025, GCN 43213),
and Konus Wind (D. Frederiks et al. 2025, GCN 43214).
The spectroscopic redshift of GRB 251222A is found to be 3.171 by VLT/X-shooter (A. Saccardi et al. 2025, GCN 43204).
The Fermi GBM on-ground location is consistent with the position reported by other instruments.
The angle from the Fermi LAT boresight is 83 degrees.
The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 83 s (50-300 keV). The time-averaged spectrum
from T0-2.2 to T0+91.7 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.26 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 118 +/- 1 keV.
The event fluence (10-1000 keV) in this time interval is
(1.09 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+54 s in the 10-1000 keV band is 9.5 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak= 64.9 +/- 0.8 keV, alpha = -0.84 +/- 0.01 and beta = -2.0 +/- 0.02.
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/"