[vsnet-grb-info 20758] Konus-Wind observation of GRB 180623A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22856
SUBJECT: Konus-Wind observation of GRB 180623A
DATE:    18/06/26 12:44:39 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 180623A
(Swift detection: Page et al., GCN Circ. 22828;
Swift-BAT refined analysis: Barthelmy et al., GCN Circ. 22833)
triggered Konus-Wind at T0=60141.775 s UT (16:42:21.775).

The burst light curve shows a multipeaked structure
started at ~T0-69 s with a total duration of ~114 s.
The emission is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 3.15(-0.24,+0.28)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+2.208 s,
of 2.94(-0.98,+1.01)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+49.408 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 = -1.03(-0.16,+0.17)
and Ep = 233(-33,+48) keV (chi2 = 63/70 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 = 61/69 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model
with  alpha = -0.78(-0.17,+0.19)
and Ep = 390(-63,+91) keV (chi2 = 59/70 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.3
(chi2 = 59/69 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180623_T60141/

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