GCN Circular 39726
Subject
GRB 250313A: Fermi GBM Detection
Event
Date
2025-03-15T02:17:47Z (8 months ago)
From
eliza.neights@gmail.com
Via
Web form
Eliza Neights (George Washington University, NASA Goddard Space Flight Center), M. Godwin (UAH), C. Meegan (UAH) and O.J. Roberts (USRA) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 14:34:33.69 UT on 13 March 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 250313A (trigger 763569278/250313607), which was also detected by Fermi LAT (Di Lalla et al. 2025, GCN 39711), AstroSat CZTI (Dasgupta et al. 2025, GCN 39714),
SVOM/GRM (Wang et al. 2025, GCN 39716), and Konus-Wind (Frederiks et al. 2025, GCN 39721).
The Fermi GBM Final Position location is consistent with the Fermi LAT position.
The angle from the Fermi LAT boresight is 4 degrees.
The GBM light curve consists of two emission episodes, a bright pulse lasting 12 s after the trigger time and a dimmer pulse about 280 s later. The duration (T90)
is about 295.2 s (50-300 keV). The time-averaged spectrum
from T0-2.2 to T0+389.0 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.36 +/- 0.01 and the cutoff energy,
parameterized as Epeak, is 320 +/- 20 keV.
The event fluence (10-1000 keV) in this time interval is
(9.4 +/- 0.1)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.7 s in the 10-1000 keV band is 55.4 +/- 0.5 ph/s/cm^2.
The spectrum is fit about equally well by a Band function with Epeak = 280 +/- 20 keV, alpha = -1.34 +/- 0.02, and beta = -2.23 +/- 0.13.
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/"