TITLE:   GCN CIRCULAR
NUMBER:  43673
SUBJECT: GRB 260208A: Fermi GBM Observation
DATE:    26/02/09 20:09:35 GMT
FROM:    oindabimukherjee@gmail.com

O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 05:07:28.24 UT on 08 February 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260208A (trigger 792220053/260208214),
which was also detected by Fermi-LAT (F. Longo et al. 2026, GCN 43645), 
Swift XRT (S. Dichiara et al. 2026, GCN 43652), 
and NOT (Dimple et al. 2026, GCN 43662) with a spectroscopic redshift of z = 2.36.

The Fermi GBM on-ground location is consistent with the Fermi-LAT position.

The angle from the Fermi LAT boresight is 80 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 35.3 s (50-300 keV). The time-averaged spectrum
from T0-3.6 to T0+66.0 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.87 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 460 +/- 0.1 keV.

The event fluence (10-1000 keV) in this time interval is
(1.50 +/- 0.06)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+17 s in the 10-1000 keV band is 29.7 +/- 0.4 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 328 +/- 1 keV, alpha = -0.76 +/- 0.01 and beta = -2 +/- 0.01.

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/"