[vsnet-grb-info 21294] Konus-Wind observation of GRB 181028A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23393
SUBJECT: Konus-Wind observation of GRB 181028A
DATE:    18/10/30 10:36:15 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova at 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 181028A
(Fermi-LAT detection: Axelsson et al., GCN Circ. 23386;
Fermi-GBM observation: Bissaldi & Meegan, GCN Circ. 23387;
IPN Triangulation: Hurley et al., GCN Circ. 23388)
triggered Konus-Wind at T0=50984.309 s UT (14:09:44.309).

The burst light curve shows a multipeaked structure
which starts at ~T0-2 s and has a total duration of ~38 s.
The emission is seen up to ~4 MeV.

As observed by Konus-Wind, the burst
had a fluence of 3.43(-0.18,+0.20)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+26.064 s,
of 4.06(-1.01,+1.03)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+40.704 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.72(-0.10,+0.11)
and Ep = 286(-22,+26) keV (chi2 = 53/70 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.6
(chi2 = 53/69 dof).

The spectrum near the maximum count rate
(measured from T0+24.320 to T0+32.512 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model
with  alpha = -0.39(-0.23,+0.27)
and Ep = 292(-37,+49) keV (chi2 = 70/70 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.1
(chi2 = 70/69 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB181028_T50984/

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