[vsnet-grb-info 16856] Konus-Wind observation of GRB 150811B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18137
SUBJECT: Konus-Wind observation of GRB 150811B
DATE:    15/08/13 13:43:58 GMT
FROM:    Anastasia Tsvetkova at Ioffe Institute  <tsvetkova 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:

The short-duration, hard-spectrum, intense GRB 150811B
(Fermi GBM detection: Jenke, GCN 18130;
IPN triangulation: Golenetskii et al., GCN 18133)
triggered Konus-Wind at T0=73329.515 s UT (20:22:09.515).

The burst light curve shows a single pulse with a duration of ~0.7 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 9.08(-1.11,+1.22)x10^-6 erg/cm2,
and a 16-ms peak energy flux, measured from T0+0.232 s,
of 2.89(-0.92,+0.95)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.35(-0.24,+0.29),
and Ep = 1197(-220,+299) keV (chi2 = 28/27 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -2.51 (chi2 = 28/26 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150811_T73329/

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