TITLE:   GCN CIRCULAR
NUMBER:  42037
SUBJECT: GRB 251001A: Fermi GBM Detection
DATE:    25/10/01 14:15:23 GMT
FROM:    Marianna Dafčíková at Masaryk University <500025@mail.muni.cz>

M. Dafcikova (MUNI), S. Lesage (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 02:40:56.95 UT on 01 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251001A (trigger 780979261/251001112).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 224.44, Dec = -56.23 (J2000 degrees, equivalent to
J2000 14h 57m, -56d 13'), with a statistical uncertainty of 1.79 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 116 degrees.

The GBM light curve consists of two peaks with a duration (T90)
of about 7 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+8.640 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.63 +/- 0.08 and the cutoff energy,
parameterized as Epeak, is 138 +/- 7 keV.

The event fluence (10-1000 keV) in this time interval is
(4.4 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+6.0 s in the 10-1000 keV band is 24.8 +/- 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/"