TITLE:   GCN CIRCULAR
NUMBER:  44179
SUBJECT: GRB 260401A: Fermi GBM Observation
DATE:    26/04/01 23:33:42 GMT
FROM:    Daniel Fernandez at University of Alabama In Huntsville (UAH) <df0062@uah.edu>

D. Fernandez (UAH), M. Dafčíková (MUNI) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 10:53:26.00 UT on 01 April 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260401A (trigger 796733611/260401454),
which was also detected by MAXI (T. Usuki et al. 2026, GCN 44176).
The Fermi GBM on-ground location (GCN 44174) is consistent with the MAXI position.

The angle from the Fermi LAT boresight is 60 degrees.

The GBM light curve consists of a bright emission episode with multiple peaks with a duration (T90)
of about 27 s (50-300 keV). The time-averaged spectrum
from T0-0.8 to T0+32.1 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.78 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 239 +/- 1 keV.

The event fluence (10-1000 keV) in this time interval is
(1.80 +/- 0.02)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+7.5 s in the 10-1000 keV band is 21.1 +/- 0.4 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/"