GCN Circular 43573

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

"At 20:02:32.57 UT on 27 January 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260127B (trigger 791236957/260127835).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 190.42, Dec = 56.88 (J2000 degrees, equivalent to
J2000 12h 41m, +56d 52'), with a statistical uncertainty of 5.21 degrees.
(radius, 1-sigma containment, statistical only; there is additionally a
systematic error which we have characterized as a mixture of two Gaussians,
one with a radius of 1.8 degrees (52% contribution) and one with a radius
of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]).

The angle from the Fermi LAT boresight is 109 degrees.

The GBM light curve displays a single short peak with a duration (T90)
of about 1 s (50-300 keV). The time-averaged spectrum
from T0-0.1 to T0+0.3 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.11 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 710 +/- 30 keV.


The event fluence (10-1000 keV) in this time interval is
(1.29 +/- 0.09)E-06 erg/cm^2. The 64-ms peak photon flux measured
starting from T0+0.064 s in the 10-1000 keV band is 22 +/- 2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 570 +/- 20 keV, alpha = -0.040 +/- 0.002 and beta = -2 +/- 0.1.


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/"