[vsnet-grb-info 16793] Konus-Wind observation of GRB 150724B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18074
SUBJECT: Konus-Wind observation of GRB 150724B
DATE:    15/07/27 14:09:55 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 long-duration, hard-spectrum GRB 150724B
(Fermi-LAT detection: Bissaldi, Racusin & Moretti, GCN 18065;
Fermi GBM detection: Veres, Connaughton & Meegan, GCN 18066)
triggered Konus-Wind at T0=67574.792 s UT (18:46:14.792).

The burst light curve shows  a double-peaked structure
which starts ~30 s before the trigger and has a total duration of ~41 s.
The emission is seen up to ~5 MeV.

As observed by Konus-Wind, the burst
had a fluence of 3.63(-0.29,+0.69)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+2.064 s,
of 6.01(-1.60,+1.62)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

Only the brightest part of the burst is covered by the
KW triggered mode data and, therefore, available for
the multi-channel spectral analysis. The time-averaged
spectrum measured from T0 to T0+8.448 s
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.65(-0.11,+0.12),
and Ep = 663(-69,+82) keV (chi2 = 77/73 dof).
Fitting by the GRB (Band) function yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -3.0 (chi2 = 77/72 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150724_T67574/

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