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/"
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