GCN Circular 40346
Subject
GRB 250504A: Fermi GBM Observation
Date
2025-05-05T08:00:47Z (13 days ago)
From
Elisabetta Bissaldi at Politecnico and INFN Bari <elisabetta.bissaldi@ba.infn.it>
Via
Web form
S. Bala (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 23:25:54.78 UT on 04 May 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250504A (trigger 768093959/250504976),
which was also detected by Swift BAT (M. J. Moss et al. 2025, GCN 40343).
The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 111 degrees.
The GBM light curve consists of multiple peaks with a duration (T90)
of about 49 s (50-300 keV). The time-averaged spectrum
from T0+0.003 to T0+59.393 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.06 +/- 0.08 and the cutoff energy,
parameterized as Epeak, is 621 +/- 130 keV.
The event fluence (10-1000 keV) in this time interval is
(1.20 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+10 s in the 10-1000 keV band is 3.6 +/- 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/"