TITLE:   GCN CIRCULAR
NUMBER:  41190
SUBJECT: GRB 250728A: Fermi GBM Observation
DATE:    25/07/28 22:25:38 GMT
FROM:    Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov>

U. Pathak (IIT Bombay), V. Sharma (NASA GSFC/UMBC) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 09:25:45.57 UT on 28 July 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250728A (trigger 775387550/250728393),
which was also detected by Swift/BAT-GUANO (Samuele Ronchini et al. 2025, GCN 41185).
The Fermi GBM on-ground location is consistent with the Swift/BAT-GUANO position.

The angle from the Fermi LAT boresight is 80 degrees.

The GBM light curve of a short complex pulse with a duration (T90)
of about 0.6 s (50-300 keV). 

The time-averaged spectrum from T0-0.58 to T0+0.32 s is best fit by
a power law function. The power law index is -1.6 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(3.5 +/- 0.5)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0-0.064 s in the 10-1000 keV band is 7 +/- 1.2 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/"