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GCN Circular 22461

Subject
Konus-Wind observation of GRB 180305A
Date
2018-03-06T14:42:58Z (6 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, A. Tsvetkova, A. Lysenko, A.Kozlova, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, bright GRB 180305A
(Fermi-LAT detection: Axelsson and E. Bissaldi, GCN Circ. 22457;
Fermi-GBM detection: Veres and von Kienlin, GCN Circ. 22458)
triggered Konus-Wind at T0=33967.647 s UT (09:26:07.647).

The burst light curve shows a single emission episode
which starts at ~T0-2.4 s and has a total duration of ~44 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180305_T33967/

As observed by Konus-Wind, the burst
had a fluence of 8.43(-0.58,+0.59)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+3.168 s,
of 2.02(-0.32,+0.32)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+16.128 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 = -0.51(-0.09,+0.10),
the high energy photon index beta = -2.41(-0.17,+0.13),
the peak energy Ep = 348(-27,+30) keV
(chi2 = 139/97 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+4.352 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 = -0.25(-0.15,+0.17),
the high energy photon index beta = -2.59(-0.44,+0.23),
the peak energy Ep = 467(-56,+64) keV
(chi2 = 113/81 dof).

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