TITLE:   GCN CIRCULAR
NUMBER:  43546
SUBJECT: GRB 260127A: Fermi GBM Observation
DATE:    26/01/28 18:26:39 GMT
FROM:    atrigg2@lsu.edu

A. C. Trigg (NPP ORAU, NASA MSFC) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 17:51:07.74 UT on 27 January 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260127A (trigger 791229072/260127744),
which was also detected by Swift BAT and XRT (N. J. Klingler et al. 2026, GCN 43529).
The Fermi GBM real-time localization (GCN 43528) is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 88 degrees.

The GBM light curve single emission episode with a duration (T90)
of about 36 s (50-300 keV). The time-averaged spectrum
from T0-15 to T0+32 s is best fit by
a power law function.
The power law index is -1.55 +/- 0.04.
A Comptonized model fits the spectra equally well with power law index is -1.29 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 490 +/- 25 keV.

The event fluence (10-1000 keV) in this time interval is
(3.8 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.32 s in the 10-1000 keV band is 2.7 +/- 0.5 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/"