[vsnet-grb-info 19348] Konus-Wind observation of GRB 170428A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21045
SUBJECT: Konus-Wind observation of GRB 170428A
DATE:    17/04/28 18:30:50 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin at mail.ioffe.ru>

A. Tsvetkova, S. Golenetskii, R. Aptekar, D. Frederiks, D. Svinkin,
P. Oleynik, M. Ulanov, A. Lysenko, A.Kozlova, and T. Cline
on behalf of the Konus-Wind team, report:

The short-duration, bright GRB 170428A
(Swift-BAT detection: Beardmore et al., GCN Circ. 21042)
triggered Konus-Wind at T0=33218.719 s UT (09:13:38.719).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.02 s and has a total duration of ~0.14 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170428_T33218/

As observed by Konus-Wind, the burst
had a fluence of 4.20(-0.90,+0.91)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.056 s,
of 5.00(-1.52,+1.53)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+0.128 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.47(-0.21,+0.28),
the high energy photon index beta = -2.46(-7.54,+0.52),
the peak energy Ep = 982(-355,+394) keV (chi2 = 31/37 dof).

Fitting this spectrum by a power law with exponential cutoff model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields
alpha = -0.53(-0.18,+0.21) and
Ep = 1134(-268,+368) keV (chi2 = 33/38 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.