TITLE:   GCN CIRCULAR
NUMBER:  18198
SUBJECT: Konus-Wind observation of GRB 150818A
DATE:    15/08/24 09:58:14 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

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

The long-duration GRB 150818A (Swift-BAT trigger #652603:
D'Elia, et al., GCN Circ. 18152; Palmer, et al., GCN Circ. 18157)
was detected by Konus-Wind in the waiting mode.

The burst light curve shows a single pulse
with a total duration of about 47 s.

As observed by Konus-Wind, the burst had a fluence of
5.3(-0.6,+0.7)x10^-6 erg/cm2 and a 2.944-s peak flux,
measured from ~T0(BAT)-3.3 s, of 1.8(-0.3,+0.4)x10^-7 erg/cm2/s
(both in the 20 - 1000 keV energy range).

Modeling the K-W 3-channel time-integrated spectrum
(from T0(BAT)-6.2 s to T0(BAT)+40.9 s)
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.4(-0.2,+0.6) and Ep = 100 (-18,+29) keV.

The K-W light curve of this burst is available at
http://www.ioffe.ru/LEA/GRBs/GRB150818A/

Assuming the redshift z=0.282 (Sanchez-Ramirez, et al., GCN 18177)
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.27, and Omega_Lambda = 0.73,
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is ~1.0x10^51 erg,
the peak luminosity L_iso is ~3.6x10^49 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is ~128 keV.

All the quoted errors are at 1 sigma confidence level.
All the quoted values are preliminary.