[vsnet-grb-info 15430] Konus-Wind observation of GRB 140818A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16719
SUBJECT: Konus-Wind observation of GRB 140818A
DATE:    14/08/19 14:37:57 GMT
FROM:    Valentin Pal'shin at Ioffe Inst  <val at mail.ioffe.ru>

S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

A long duration GRB 140818A (MAXI/GSC detection: Honda et al., GCN 
16702, 16705; Fermi-GBM detection: Roberts, GCN 16708) triggered 
Konus-Wind at T0=19880.472 s UT (05:31:20.472).

The burst light curve shows a rather weak pulse at ~T0-83 s followed by 
the main emission episode at ~T0-15 s. The total duration of the burst 
is ~126 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/GRB140818_T19880/

As observed by Konus-Wind, the burst
had a fluence of 3.68(-0.21,+0.22)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+24.304 s,
of (2.29+/-0.49)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+41.216 s)
is best fit in the 20 keV - 3 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.11 (-0.13,+0.14)
and Ep = 219 (-21,+26) keV (chi2 = 68/68 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 68/67 dof)

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