TITLE:   GCN CIRCULAR
NUMBER:  42846
SUBJECT: GRB 251121A: Fermi GBM Observation
DATE:    25/11/26 20:32:32 GMT
FROM:    Angus Jameson <abj0023@uah.edu>

S. Bala (USRA), A. Jameson (UAH), and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 16:30:58.99 UT on 21 November 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251121A (trigger 785435463/251121688),
which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2025 GCN 42795).
The Fermi GBM on-ground location (GCN 42790) is consistent with the Swift/BAT-GUANO position.

The angle from the Fermi LAT boresight is 100 degrees.

The GBM light curve single peak with a duration (T90)
of about 0.3 s (50-300 keV). The time-averaged spectrum
from T0-0.2 to T0+0.3 s is best fit by
a simple power law function with index -1.31 +/- 0.07.

The event fluence (10-1000 keV) in this time interval is
(2.8 +/- 0.3)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band is 5 +/- 1 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/"