[vsnet-grb-info 21095] Konus-Wind observation of GRB 180828A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23193
SUBJECT: Konus-Wind observation of GRB 180828A
DATE:    18/08/30 20:51:39 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 180828A (Swift-BAT detection:
Beardmore et al., GCN 23182; Markwardt et al., GCN 23188;
Fermi-GBM observation: Roberts & Meegan, GCN 23183;
AstroSat-CZTI detection: Khanam et al., GCN 23191)
triggered Konus-Wind at T0=68250.016 s UT (18:57:30.016).

The burst light curve shows a multipeaked structure
which starts at ~T0-6 s and has a duration of ~14.7 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.41(-0.17,+0.17)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+7.456 s,
of 1.57(-0.24,+0.26)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+15.104 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.50(-0.12,+0.12)
and Ep = 341(-21,+24) keV (chi2 = 72/88 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 70/87 dof).

The spectrum near the maximum count rate
(measured from T0+6.912 to T0+15.104 s)
is best fit in the 20 keV - 10 MeV range
by the CPL model with  alpha = -0.36(-0.23,+0.26)
and Ep = 395(-45,+59) keV (chi2 = 61/86 dof).
Fitting by the GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.5
(chi2 = 61/85 dof).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180828_T68250/

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