TITLE:   GCN CIRCULAR
NUMBER:  43384
SUBJECT: GRB 260111A: Fermi GBM Observation
DATE:    26/01/13 02:51:56 GMT
FROM:    Eva MP at INAOE <eva.palafox@gmail.com>

Eva Palafox (INAOE) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 16:33:14.01 UT on 11 January 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260111A (trigger 789841999/260111690).
which was also detected by Swift/BAT (S. Ronchini et al. 2026, GCN 43377).
The Fermi GBM on-ground location (GCN 43370) is consistent with the Swift/BAT position.

The angle from the Fermi LAT boresight is 14.4 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 31 s (50-300 keV). The time-averaged spectrum
from T0-18 to T0+52 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.7 +/- 0.3 and the cutoff energy,
parameterized as Epeak, is 140 +/- 30 keV.

The event fluence (10-1000 keV) in this time interval is
(2.3 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.70 s in the 10-1000 keV band is 2.4 +/- 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/"