TITLE:   GCN CIRCULAR
NUMBER:  41917
SUBJECT: GRB 250920C: Fermi GBM Observation
DATE:    25/09/20 20:46:55 GMT
FROM:    Bagrat Mailyan at Florida Tech <mbagrat@gmail.com>

B. Mailyan (Florida Tech) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 15:25:17.06 UT on 20 September 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250920C (trigger 780074722/250920643)
which was also detected by Swift BAT (R. Gupta et al. 2025, GCN 41904).
The Fermi GBM Final Real-time Localization (GCN 41903) is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 94 degrees.

The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 36.6 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+37.377 s is best fit by
a Band function with Epeak = 117 +/- 4 keV,
alpha = -0.76 +/- 0.04, and beta = -2.34 +/- 0.05.

The event fluence (10-1000 keV) in this time interval is
(2.97 +/- 0.04)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+26 s in the 10-1000 keV band is 25.1 +/- 0.5 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/"