[vsnet-grb-info 20768] Konus-Wind observation of GRB 180626B

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22866
SUBJECT: Konus-Wind observation of GRB 180626B
DATE:    18/06/27 13:26:58 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 short-duration GRB 180626B
(IPN Triangulation: Hurley et al., GCN Circ. 22863)
triggered Konus-Wind at T0=6442.786 s UT (01:47:22.786).

The burst light curve shows a single pulse which starts
at ~T0-0.1 s and has a total duration of ~0.3 s.
The emission is seen up to ~2 MeV.

As observed by Konus-Wind, the burst
had a fluence of 7.69(-1.24,+1.35)x10^-7 erg/cm2,
and a 16-ms peak flux, measured from T0+0.004 s,
of 7.35(-2.79,+3.01)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+0.192 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 = -0.13(-0.54,+0.73)
and Ep = 218(-43,+60) keV (chi2 = 23/26 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 = 23/25 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+0.064 s)
is best fit in the 20 keV - 4 MeV range
by a power law with exponential cutoff model
with  alpha = -0.08(-0.59,+0.87)
and Ep = 294(-70,+116) keV (chi2 = 14/16 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 = 14/15 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180626_T06442/

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