[vsnet-grb-info 19339] Konus-Wind observation of GRB 170424A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21036
SUBJECT: Konus-Wind observation of GRB 170424A
DATE:    17/04/25 17:33:31 GMT
FROM:    Anastasia Tsvetkova at Ioffe Institute  <tsvetkova at mail.ioffe.ru>

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

The long-duration GRB 170424A
(Fermi-LAT detection: Omodei & Vianello, GCN 21032;
Fermi GBM detection: Stanbro, von Kienlin & Meegan, GCN 21033)
triggered Konus-Wind at T0=36769.094 s UT (10:12:49.094).

The burst light curve shows a single pulse  which started
at ~T0-20 s and lasted until ~T0+42 s (the total duration is ~62 s).
The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst
had a fluence of 3.46(-0.32,+0.44)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0-0.046 s,
of 2.81(-1.05,+1.11)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+41.216 s)
is best fit in the 20 keV - 18 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.91(-0.19,+0.23),
and Ep = 353(-70,+111) keV (chi2 = 82/98 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.01 (chi2 = 82/97 dof).

The spectrum near the peak count rate
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.77(-0.23,+0.33),
the high energy photon index beta = -3.30(-6.70,+1.17),
the peak energy Ep = 446(-127,+170) keV,
chi2 = 108/97 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170424_T36769/

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