GCN Circular 31964
Subject
Konus-Wind detection of GRB 220427A
Date
2022-04-28T14:20:52Z (2 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long GRB 220427A (Swift detection: D'Ai et al., GCN Circ. 31960)
triggered Konus-Wind (KW) at T0=75645.009 s UT (21:00:45.009).
The burst light curve shows a single pulse,
which starts at ~T0-3 s and has a total duration of ~15 s.
The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB220427_T75645/
As observed by Konus-Wind, the burst had
a fluence of (1.0 �� 0.3)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 0.256 s,
of (2.5 �� 0.7)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
A time-averaged spectrum of the burst (measured from T0 to T0+8.448 s)
is well fit in the 20 keV - 15 MeV range
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.04(-0.30,+0.43) and Ep = 503(-204,+757) keV (chi2 = 77/97 dof).
A fit to this spectrum by the Band GRB function is poorly constrained,
it results in the best fit values of alpha~-0.6, Ep~260 keV, and
the high energy photon index beta ~ -2.0 (chi2 = 77/96 dof).
All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.