GCN Circular 40799

O. Mukherjee (USRA) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 16:07:09.92 UT on 20 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB250620C (trigger 772128434/250620672).

The on-ground calculated location, using the Fermi GBM trigger data,
is RA = 142.61, Dec = 54.96 (J2000 degrees, equivalent to
J2000 9h 30m, +54d 57'), with a statistical uncertainty of 1.00 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 124 degrees.

The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 32 s (50-300 keV). The time-averaged spectrum
from T0 to T0+35.7 s is best fit by
a Band function with Epeak= 371 +/- 15 keV, alpha = -0.93 +/- 0.02 and beta = -2.6 +/- 0.2.

The event fluence (10-1000 keV) in this time interval is
(6.64 +/- 0.07)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.96 s in the 10-1000 keV band is 50.1 +/- 0.7 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/"