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GCN Circular 22548

Subject
Konus-Wind observation of GRB 180316A
Date
2018-03-26T15:10:45Z (6 years ago)
From
Anastasia Tsvetkova at Ioffe Institute <tsvetkova@mail.ioffe.ru>
A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks,
M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 180316A
(Swift detection of a burst: Melandri et al., GCN 22500;
Cummings et al., GCN 22512)
triggered Konus-Wind at T0=17845.869 s UT (04:57:25.869).

The burst light curve shows a single emission episode
which starts at ~T0-13 s and has a total duration of ~29 s.
The emission is seen up to ~1.2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 1.43(-0.21,+0.38)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+2.976 s,
of 2.77(-1.16,+1.49)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+16.640 s)
is best fit in the 20 keV - 1.2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with�� alpha = -1.23(-0.23,+0.27),
and Ep = 439(-139,+424) keV (chi2 = 74/60 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -1.87 (chi2 = 74/59 dof).

The spectrum near the peak count rate
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model
with�� alpha = -1.19(-0.22,+0.26),
and Ep = 498(-165,+498) keV (chi2 = 54/61 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index:
beta < -1.75 (chi2 = 53/60 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180316_T17845/

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