[vsnet-grb-info 20457] Konus-Wind observation of GRB 180326A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22553
SUBJECT: Konus-Wind observation of GRB 180326A
DATE:    18/03/27 14:23:52 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 180326A
(IPN Triangulation: Hurley et al., GCN 22550)
triggered Konus-Wind at T0=12367.064 s UT (03:26:07.064).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.2 s and has a total duration of ~20.6 s.
The emission is seen up to ~6 MeV.

As observed by Konus-Wind, the burst
had a fluence of 2.19(-0.30,+0.36)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.336 s,
of 9.16(-2.36,+2.52)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+16.640 s)
is best fit in the 20 keV - 6 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.55(-0.20,+0.24)
and Ep = 767(-142,+200) keV (chi2 = 80/80 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.0
(chi2 = 80/79 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 - 6 MeV range
by a power law with exponential cutoff model
with alpha = -0.61(-0.20,+0.23)
and Ep = 806(-151,+208) keV (chi2 = 85/80 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 = 85/79 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180326_T12367/
We note the MAXI J1820+070 activity seen in the waiting mode data.

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