TITLE:   GCN CIRCULAR
NUMBER:  40621
SUBJECT: GRB 250601A: Fermi GBM Observation
DATE:    25/06/03 15:42:16 GMT
FROM:    Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov>

V. Sharma (NASA-GSFC/UMBC) and C. Meegan (UAH) report on behalf of the 
Fermi Gamma-ray Burst Monitor Team:

"At 17:29:35 UT on 1 Jun 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250601A (trigger 770491780 / 250601729).
which was also detected by Swift/BAT-GUANO (J. DeLaunay et al. 2025, GCN 40600) 
and Swift/XRT (K.L. Page et al. 2025, GCN 40604). 
The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.

The angle from the Fermi LAT boresight is 24 degrees.

The GBM light curve consists of main emission episode with a 
duration (T90) of about 3 s (50-300 keV). The time-averaged 
spectrum from T0-0.5 to T0+2.4 s is best fit by a power law 
function with an exponential high-energy cutoff. The 
power law index is -0.58 +/- 0.1 and the cutoff energy, 
parameterized as Epeak, is 873 +/- 142 keV.

The event fluence (10-1000 keV) in this time interval is
(2.7 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+1 s in the 10-1000 keV band is 4.9 +/- 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/"