GCN Circular 41411
Subject
GRB 250818A: Fermi GBM Observation
Event
Date
2025-08-18T15:01:48Z (7 days ago)
Edited On
2025-08-18T15:03:55Z (7 days ago)
From
Cuán de Barra at UCD <cuan.debarra@ucdconnect.ie>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Cuán de Barra at UCD <cuan.debarra@ucdconnect.ie>
Via
Web form
C. de Barra (University College Dublin) and C. Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 01:31:23.00 UT on 18 August 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250818A (trigger 777173487/250818063)
which was also detected by Swift BAT (S. B. Cenko et al. 2025, GCN 41403).
The Fermi GBM on-ground location is consistent with the Swift BAT position.
The angle from the Fermi LAT boresight is 146 degrees.
The GBM light curve consists of multiple emission episodes with a duration (T90)
of about 101 s (50-300 keV). The time-averaged spectrum
from T0-9.2 to T0+94.2 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.83 +/- 0.14 and the cutoff energy,
parameterized as Epeak, is 83 +/- 5 keV.
The event fluence (10-1000 keV) in this time interval is
(1.62 +/- 0.06)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+78 s in the 10-1000 keV band is 8.8 +/- 0.7 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/"