TITLE:   GCN CIRCULAR
NUMBER:  39795
SUBJECT: GRB 250321A: Fermi GBM Observation
DATE:    25/03/21 06:04:23 GMT
FROM:    A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca@unitn.it>

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

"At 00:42:39.02 UT on 21 March 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250321A (trigger 764210564/250321030),
which was also detected by Swift BAT (Gupta et al. 2025, GCN 39794).
The Fermi GBM on-ground location is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 39 degrees.

The GBM light curve shows one main pulse with a duration (T90)
of about 6 s (50-300 keV). The time-averaged spectrum
from T0-0.5 to T0+7.2 s is best fit by 
a power law function with an exponential high-energy cutoff.
The power law index is -0.83 +/- 0.20 and the cutoff energy,
parameterized as Epeak, is 101 +/- 12 keV.

The event fluence (10-1000 keV) in this time interval is
(1.04 +/- 0.08)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-0.13 s in the 10-1000 keV band is 4.7 +/- 0.3 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/"