TITLE:   GCN CIRCULAR
NUMBER:  40664
SUBJECT: GRB 250609A: Fermi GBM Observation
DATE:    25/06/10 09:59:45 GMT
FROM:    Christian Malacaria at INAF-OAR <cmalacaria.astro@gmail.com>

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

"At 08:47:18.61 UT on 09 June 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250609A (trigger 771151643/250609366).
which was also detected by Swift/BAT-GUANO (DeLaunay et al. 2025, GCN 40658).
The Fermi GBM on-ground location was reported by the Fermi-GBM team in GCN 40652.

The angle from the Fermi LAT boresight is 81 degrees.

The GBM light curve consists of a single emission episode with a duration (T90)
of about 1 s (50-300 keV). The time-averaged spectrum
from T0-5.5 to T0+1.7 s is best fit by
a simple power law function with index -1.3 +/- 0.1.

The event fluence (10-1000 keV) in this time interval is
(4.5 +/- 0.9)E-07 erg/cm^2. The 64-ms peak photon flux measured
starting from T0-0.13 s in the 10-1000 keV band is 4 +/- 1 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/"