[vsnet-grb-info 20240] Konus-Wind observation of GRB 180111A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22336
SUBJECT: Konus-Wind observation of GRB 180111A
DATE:    18/01/15 10:37:21 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin at 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 bright long-duration GRB 180111A
(Swift-BAT detection: Lien et al., GCN Circ. 22318;
AGILE-MCAL detection: Verrecchia et al., GCN Circ. 22321)
triggered Konus-Wind at T0=60130.616 s UT (16:42:10.616).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.2 s and has a total duration of ~61 s.
The emission is seen up to ~6 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180111_T60130/

As observed by Konus-Wind, the burst
had a fluence of 8.44(-0.57,+0.64)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.018 s,
of 1.06(-0.21,+0.22)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+39.424 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.94(-0.06,+0.06)
and Ep = 894(-95,+113) keV (chi2 = 106/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 106/97 dof).

The spectrum near the maximum count rate
(measured from T0+0.000 to T0+7.424 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
with  alpha = -0.51(-0.08,+0.09)
and Ep = 895(-82,+94) keV (chi2 = 89/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.8
(chi2 = 89/97 dof).

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