GCN Circular 42047

Eliza Neights (GWU, NASA GSFC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 14:17:19.05 UT on 01 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251001B (trigger 781021044/251001595)
which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 42039
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 ).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 53 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 19 s (50-300 keV). The time-averaged spectrum
from T0-3.7 to T0+16.7 s is best fit by
a Comptonized function with index 0.22 +/- 0.03 and peak energy 107 +/- 5 keV.

The event fluence (10-1000 keV) in this time interval is
(1.3 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.7 s in the 10-1000 keV band is 1.4 +/- 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/"