GCN Circular 45976

O. Mukherjee (USRA), L. Scotton (UAH) and P. Veres (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 16:05:05.10 UT on 17 October 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 261017A (trigger 813945910/261017670),
which was also detected by Swift BAT (M. H. Siegel et al. 2026, GCN 45974
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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 67 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 9.2 s (50-300 keV). The time-averaged spectrum
from T0-0.6 to T0+10 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.44 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 1024 +/- 22 keV.

The event fluence (10-1000 keV) in this time interval is
(1.22 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.26 s in the 10-1000 keV band is 4.3 +/- 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/"