GCN Circular 18200

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 150821A (Swift-BAT trigger #652847:
Troja et al., GCN 18186
Not found
 
 
; Stamatikos et al., GCN 18196
Not found
 
 
;
Fermi GBM detection: Roberts, GCN 18190
Not found
 
 
)
triggered Konus-Wind at T0=35074.166 s UT (09:44:34.166).

The burst light curve shows a single multi-peaked pulse
which started at ~T0-1.4 s and had a total duration of ~161.6 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 9.16(-2.22,+2.38)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+4.768 s,
of 3.68(-1.02,+1.27)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+164.096 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.47 (-0.09,+0.15),
the high energy photon index beta = -2.21 (-7.79,+0.29),
the peak energy 350 (-125,+202) keV
(chi2 = 129/97 dof)

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.07 (-0.10,+0.15),
the high energy photon index beta = -3.13 (-6.87,+0.80),
the peak energy 327 (-66,+58) keV
(chi2 = 91/91 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150821_T35074/
The background variations in the soft KW band are due to solar activity.

Assuming the redshift z=0.755 (D'Elia et al., GCN 18187
Not found
 
 
)
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 ~1.4x10^53 erg,
the peak luminosity L_iso is ~1.0x10^52 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is ~614 keV.

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