GCN Circular 39018
Subject
GRB 250121A: Fermi GBM Observation
Date
2025-01-23T20:33:41Z (18 days ago)
From
Matt Godwin <msg0028@uah.edu>
Via
Web form
Matt Godwin (UAH) and C.Meegan (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 23:36:05.78 UT on 21 January 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250121A (trigger 759195370/250121983).
which was also detected by Fermi-LAT (Holzmann Airasca et al. 2025, GCN 39010).
The Fermi GBM on-ground location is consistent with the Fermi-LAT position. (Fermi GBM Team et al. 2025, GCN 39006)
The angle from the Fermi LAT boresight is 15 degrees.
This burst was also independently detected by INTEGRAL SPI-ACS.
The GBM light curve consists of one peak with a duration (T90)
of about 5.2 s (50-300 keV). The time-averaged spectrum
from T0-0.4 to T0+5.8 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.65 +/- 0.05 and the cutoff energy,
parameterized as Epeak, is 230 +/- 10 keV.
The event fluence (10-1000 keV) in this time interval is
(5.8 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.32 s in the 10-1000 keV band is 14.0 +/- 0.3 ph/s/cm^2.
A Band function fits the spectrum equally well
with Epeak= 210 +/- 20 keV, alpha = -0.59 +/- 0.07 and beta = -2.5 +/- 0.3.
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/"