TITLE: GCN CIRCULAR NUMBER: 40717 SUBJECT: GRB 250612B: Fermi GBM Observation DATE: 25/06/13 06:34:50 GMT FROM: Rushikesh Sonawane at IISER, TVM rushikesh23@iisertvm.ac.in
R. Sonawane (IISER, TVM) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 12:27:56.19 UT on 12 June 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250612B (trigger 771424081/250612519). which was also detected by EP-WXT (Hua et al. 2025, GCN 40700). The Fermi GBM on-ground location is consistent with the EP-WXT position.
The angle from the Fermi LAT boresight is 68 degrees.
The GBM light curve consists of single emission episode with a duration (T90) of about 10.8 s (50-300 keV). The time-averaged spectrum from T0-4.4 to T0+18.2 s is best fit by a Band function with Epeak = 47.80 +/- 1.53 keV, alpha = -0.92 +/- 0.09, and beta = -3.47 +/- 0.39.
A Comp model fits the spectrum equally well, with a power-law index = –0.98 +/- 0.07 and cutoff energy parameterized as Epeak = 49.14 +/- 1.26 keV.
The event fluence (10-1000 keV) in this time interval is (5.2 +/- 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 12.1 +/- 0.3 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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