GCN Circular 42520
Subject
GRB 251028A: Fermi GBM Observation
Event
Date
2025-10-29T20:08:12Z (2 days ago)
From
Peter Veres at University of Alabama in Huntsville <veresp@gmail.com>
Via
Web form
P. Veres (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 03:26:31.86 UT on 28 October 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251028A (trigger 783314796/251028143) which was also detected by MAXI (Negoro et al. 2025, GCN 42498) and Glowbug (Cheung et al. 2025, GCN 42506). The Fermi GBM on-ground location is consistent with the MAXI position.
The angle from the Fermi LAT boresight is 50 degrees.
The GBM light curve consists of multiple overlapping pulses with a duration (T90)
of about 30 s (50-300 keV). The time-averaged spectrum
from T0 to T0+39.9 s is best fit by
a Band function with Epeak = 244 +/- 14 keV,
alpha = -0.91 +/- 0.03, and beta = -2.4 +/- 0.1.
The event fluence (10-1000 keV) in this time interval is
(3.13 +/- 0.05)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+24 s in the 10-1000 keV band is 10.8 +/- 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/"