TITLE:   GCN CIRCULAR
NUMBER:  44760
SUBJECT: GRB 260601A: Fermi GBM Observation
DATE:    26/06/01 18:13:56 GMT
FROM:    A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca@unitn.it>

A. Holzmann Airasca (UniTrento and INFN Bari) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 11:00:12.44 UT on 01 June 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260601A (trigger 802004417/260601458).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 15.06, Dec = 44.38 (J2000 degrees, equivalent to
J2000 1h 0m, +44d 22'), with a statistical uncertainty of 2.03 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 30 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 0.8 s (50-300 keV). The time-averaged spectrum
from T0-0.07 to T0+0.34 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.63 +/- 0.02 and the cutoff energy,
parameterized as Epeak, is 960 +/- 30 keV.

The event fluence (10-1000 keV) in this time interval is
(2.08 +/- 0.06)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 40 +/- 1 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 750 +/- 20 keV, alpha = -0.57 +/- 0.05 and beta = -2.0 +/- 0.2.


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/"