GCN Circular 39873
Subject
Konus-Wind detection of GRB 250322A (short)
Date
2025-03-26T12:50:11Z (5 days ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The short-duration GRB 250322A
(Swift-BAT detection: Gupta et al., GCN 39835; Sadaula et al., GCN 39867;
AstroSat-CZTI detection: Tembhurnikar et al., GCN 39849)
triggered Konus-Wind at T0=57974.215 s UT (16:06:14.215).
The burst light curve shows a multipeaked structure,
which starts at T0-0.102 s and has a total duration of ~0.18 s.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250322_T57974/
As observed by Konus-Wind, the burst
had a fluence of 1.02(-0.13,+0.14)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0-0.086 s,
of 1.05(-0.24,+0.25)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
Since the brightest peak of the burst light curve
was detected before the trigger, the spectral analysis
was performed using the KW 3-channel light curve data.
Modelling the KW 3-channel time-integrated spectrum
(measured from T0-0.102 s to T0+0.078 s)
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep),
yields alpha = 0.22(-0.39,+0.52) and Ep = 472(-64,+85) keV.
Assuming the redshift z=0.42 (Fong et al., GCN 39852; Yang et al. GCN 39859)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is 4.9(-0.6,+0.7)x10^50 erg,
the peak luminosity L_iso is 7.1(-1.6,+1.7)x10^51 erg/s,
the rest-frame peak energy of the time-averaged spectrum
Ep,i,z is 670(-91,+121) keV.
With the obtained estimates, GRB 250322A is a clear outlier
in the 'Amati' relation derived for the sample of >300 long KW GRBs
with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021).
Meanwhile, in both Eiso-Ep,z and Liso-Ep,z planes, the GRB 250322A position
is consistent with short-hard (Type I) GRB population,
see http://www.ioffe.ru/LEA/GRBs/GRB250322_T57974/GRB250322A_rest_frame.pdf
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.