TITLE:   GCN CIRCULAR
NUMBER:  42513
SUBJECT: GRB 251026B: Fermi GBM Observation
DATE:    25/10/29 14:40:22 GMT
FROM:    Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>

M. Dafcikova (MUNI) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 07:18:53.33 UT on 26 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251026B (trigger 783155938/251026305).

The angle from the Fermi LAT boresight is 19 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 6 s (50-300 keV). The time-averaged spectrum
from T0-1.3 to T0+3.7 s is best fit by
a simple power law function with index -1.38 +/- 0.04.

The event fluence (10-1000 keV) in this time interval is
(7.2 +/- 0.7)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.32 s in the 10-1000 keV band is 1.6 +/- 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/"