TITLE:   GCN CIRCULAR
NUMBER:  39724
SUBJECT: GRB 250312B: Fermi GBM Observation
DATE:    25/03/15 00:56:42 GMT
FROM:    Lorenzo Scotton at UAH <lscottongcn@outlook.com>

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

"At 20:36:56.64 UT on 12 March 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250312B (trigger 763504621/250312859),
which was also localized by Swift/BAT-GUANO (J. DeLaunay et al. 2025, GCN 39708).
The Fermi GBM on-ground location was given in GCN 39692 and it is consistent 
with the Swift/BAT-GUANO localization skymap.

The angle from the Fermi LAT boresight is 105 degrees.

The GBM light curve consists of single emission with two over lapping pulses, 
with a duration (T90) of about 5.4 s (50-300 keV). The time-averaged spectrum 
from T0-1.0 to T0+5.5 s is best fit by a power law function with an exponential 
high-energy cutoff. The power law index is -1.1 +/- 0.1 and the cutoff energy,
parameterized as Epeak, is 260 +/- 50 keV.

The event fluence (10-1000 keV) in this time interval is
(2.7 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.003 s in the 10-1000 keV band is 4.4 +/- 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/"