TITLE:   GCN CIRCULAR
NUMBER:  22680
SUBJECT: Konus-Wind observation of GRB 180427A
DATE:    18/05/04 10:41:56 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova@mail.ioffe.ru>

A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 180427A
(Fermi GBM detection: Bissaldi, GCN Circ. 22678,
IPN triangulation: Hurley et al., GCN Circ. 22679)
triggered Konus-Wind at T0=38222.928 s UT (10:37:02.928).

The burst light curve shows a single pulse
which starts at ~T0-0.4 s and has a total duration of ~34.5 s.
The emission is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 5.09(-0.19,+0.21)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+5.024 s,
of 4.93(-0.81,+0.81)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+33.536 s)
is best fit in the 20 keV - 2 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.59(-0.07,+0.08),
the high energy photon index beta = -3.10(-0.24,+0.17),
the peak energy Ep = 116(-4,+4) keV
(chi2 = 78/61 dof).

The spectrum near the maximum count rate
(measured from T0+3.840 to T0+7.424 s)
is best fit in the 20 keV - 2 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = 0.49(-0.13,+0.14),
the high energy photon index beta = -3.78(-0.51,+0.30),
the peak energy Ep = 135(-5,+5) keV
(chi2 = 78/60 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180427_T38222/

There are no data available for the triggered mode 300-1200 keV band.

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