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GCN Circular 18974

Subject
Konus-Wind observation of GRB 160131A
Date
2016-02-02T15:36:05Z (8 years ago)
From
Anastasia Tsvetkova at Ioffe Institute <tsvetkova@mail.ioffe.ru>
A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, extremely hard-spectrum GRB 160131A
(Swift-BAT trigger #672236: Page & Barthelmy, GCN 18951;
Cummings  et al., GCN 18959)
triggered Konus-Wind at T0=30044.577 s UT (08:20:44.577).

The burst light curve shows a single, FRED-like pulse
with a total duration (80-1400 keV) of ~200 s.
In the softest KW energy band the emission can be traced up to ~300 s.
The emission is seen up to ~15 MeV.

As observed by Konus-Wind, the burst
had a fluence of 3.26(-0.32,+0.31)x10^-4 erg/cm2,
and a 64-ms peak energy flux, measured from T0+2.704 s,
of 2.23(-0.46,+0.46)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+162.048 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.97(-0.15,+0.24),
the high energy photon index beta = -1.56(-0.10,+0.07),
the peak energy Ep = 586(-259,+518) keV,
chi2 = 98/97 dof.

The spectrum near the peak count rate
(measured from T0+0.256 to T0+14.592 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.94(-0.18,+0.13),
the high energy photon index beta = -1.56(-0.56,+0.06),
the peak energy Ep = 1152(-438,+3060) keV,
chi2 = 135/97 dof.

Assuming the redshift z=0.972 (Malesani et al., GCN 18965;
de Ugarte Postigo, Thoene & Sanchez-Ramirez, GCN 18966;
Xu, Xin & Wang, GCN 18969)
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 ~8.3x10^53 erg,
the peak luminosity L_iso is ~1.1x10^53 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is ~1150 keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160131_T30044/

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