TITLE:   GCN CIRCULAR
NUMBER:  38887
SUBJECT: GRB 250109A: Fermi GBM Observation
DATE:    25/01/10 06:40:17 GMT
FROM:    Utkarsh Pathak at IIT Bombay <utkarshpathak.07@gmail.com>

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

"At 06:17:08.60 UT on 09 January 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250109A (trigger 758096233/250109262).
which was also detected by EP-WXT and EP-FXT (Li et al. 2025, GCN 38864).
The Fermi GBM on-ground location is consistent with the EP-FXT position.
A possible optical counterpart was also detected by SVOM/VT (Qiu et al. 2025, GCN 38872).

The angle from the Fermi LAT boresight is 72 degrees.

The GBM light curve consists of multiple weak spikes from a single emission episode 
with a duration (T90) of about 15 s (50-300 keV). The time-averaged spectrum
from T0-8.2 to T0+9.2 s is best fit by a power law function. 
The power law index is -1.57 +/- 0.05.

The event fluence (10-1000 keV) in this time interval is
(1.9 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.9 s in the 10-1000 keV band is 1.3 +/- 0.2 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/"