[vsnet-grb-info 19681] Konus-Wind observation of GRB 170724A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21425
SUBJECT: Konus-Wind observation of GRB 170724A
DATE:    17/08/08 13:17:35 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova at mail.ioffe.ru>

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

The long GRB 170724A (Swift-BAT trigger #764204: Ukwatta et al.,
GCN 21364; Sakamoto et al., GCN 21365)
was detected by Konus-Wind (KW) in the waiting mode.

The burst light curve shows two emission episodes. The first
started at at ~T0(BAT)-508.6 s with a duration of ~247 s and the
second weaker episode, which corresponds to the BAT trigger,
started at ~T0(BAT)-20 s with a duration of ~91 s.

As observed by Konus-Wind, the first episode had a fluence of
5.49(-0.24,+0.26)x10^-5 erg/cm2 and a 2.944-s peak flux,
measured from ~T0(BAT)-408.5 s, of 1.33(-0.16,+0.16)x10^-6 erg/cm2/s.
The second episode had a fluence of ~ 0.4 x10^-5 erg/cm2
(all in the 20 - 1000 keV energy range).

Modeling the KW 3-channel time-integrated spectrum of the first episode
(from ~T0(BAT)-508.6 s to ~T0(BAT)-261.3 s)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.36 (-0.78,+0.82), and Ep = 340 (-49,+77) keV.

Modeling the KW 3-channel time-integrated spectrum of the second episode
(from ~T0(BAT)-20 s to ~T0(BAT)+71.4 s)
by a simple power-law model yields a power law
index of -2.06(-0.13,+0.24), chi2=0.9/1 dof.

The KW light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB170724A/

All the quoted errors are estimated at the 1 sigma confidence level.
All the presented results are preliminary.