TITLE:   GCN CIRCULAR
NUMBER:  45816
SUBJECT: GRB 261005B: Fermi GBM Observation
DATE:    26/10/06 04:28:59 GMT
FROM:    Matt Godwin <msg0028@uah.edu>

Matt Godwin (UAH) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 21:39:13.77 UT on 05 October 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 261005B (trigger 812929158/261005902),
which was also detected by Swift BAT (T.M. Parsotan et al. 2026, GCN 45812).
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 consist of multiple peaks with a duration (T90)
of about 22 s (50-300 keV). The time-averaged spectrum
from T0-6.4 to T0+20.6 s is best fit by a power law function with an exponential high-energy cutoff.
The power law index is -0.56 +/- 0.1 and the cutoff energy, parameterized as Epeak, is 110 +/- 8 keV.

The event fluence (10-1000 keV) in this time interval is
(8 +/- 2)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+13 s in the 10-1000 keV band is 1.56 +/- 0.19 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/"