TITLE:   GCN CIRCULAR
NUMBER:  40805
SUBJECT: GRB250620A: Fermi GBM Observation
DATE:    25/06/21 23:52:54 GMT
FROM:    rhamburg@usra.edu

R. Hamburg (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 08:05:18.94 UT on 20 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250620A (trigger 772099523/250620337) which was 
also detected by Swift/BAT-GUANO (DeLaunay et al. 2025, GCN 40796).

The angle from the Fermi LAT boresight is 164 degrees.

The GBM light curve two pulses with a duration (T90)
of about 12 s (50-300 keV). The time-averaged spectrum
from T0-0.3 to T0+10 s is best fit by a simple power law 
function with index -1.6 +/- 0.2.

The event fluence (10-1000 keV) in this time interval is
(1.1 +/- 1.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+3.8 s in the 10-1000 keV band is 9 +/- 2 ph/s/cm^2.

A Band function fits the spectrum equally well with 
Epeak = 2000 +/- 200 keV, alpha = -1.08 +/- 0.03 and beta = -2.44 +/- 0.09.

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/"