TITLE:   GCN CIRCULAR
NUMBER:  40030
SUBJECT: GRB 250402A: Fermi GBM Observation
DATE:    25/04/03 17:29:10 GMT
FROM:    Matt Godwin <msg0028@uah.edu>

Jacob Smith (UAH), Utkarsh Pathak(IIT Bombay), and Matt Godwin (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 23:08:09.09 UT on 02 April 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250402A (trigger 765328094/250402964).
which was also detected by SVOM (Chen et al. 2025, GCN 40014).
The Fermi GBM on-ground location is consistent with the SVOM position.

The angle from the Fermi LAT boresight is 57 degrees.

The GBM light curve consists of a double peak with a duration (T90)
of about 44 s (50-300 keV). The time-averaged spectrum
from T0-5.1 to T0+45.1 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 115 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval is
(4.1 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+23 s in the 10-1000 keV band is 2.4 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 60 +/- 10 keV, alpha = -0.4 +/- 0.3 and beta = -2.1 +/- 0.1.

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/"