TITLE: GCN CIRCULAR NUMBER: 40473 SUBJECT: GRB 250516A: Fermi GBM Observation DATE: 25/05/16 23:59:42 GMT FROM: oindabimukherjee@gmail.com
O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 14:35:29.28 UT on 16 May 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250516A (trigger 769098934/250516608). which was also detected by Swift BAT (A. P. Beardmore et al. 2025, GCN 40467). The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 36 degrees.
The GBM light curve consists of two peaks with a duration (T90) of about 21.8 s (50-300 keV). The time-averaged spectrum from T0-1.4 to T0+25.2 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -1.26 +/- 0.07 and the cutoff energy, parameterized as Epeak, is 200 +/- 30 keV.
The event fluence (10-1000 keV) in this time interval is (4.8 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0+5.1 s in the 10-1000 keV band is 5.8 +/- 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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