[vsnet-grb-info 20330] Konus-Wind observation of GRB 180218A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22426
SUBJECT: Konus-Wind observation of GRB 180218A
DATE:    18/02/20 13:20:00 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at mail.ioffe.ru>

D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

The long GRB 180218A (IPN Triangulation: Svinkin et al., GCN 22423;
Fermi-GBM detection: Poolakkil et al., GCN 22424;
CALET Gamma-Ray Burst Monitor detection: Ishizaki et al., GCN 22425)
triggered Konus-Wind at T0=54845.382 s UT (15:14:05.382)

The burst light curve shows a single, bright, multi-peaked pulse.
The total duration of the burst is ~17 s.
The emission is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(7.6 ± 0.6)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+3.648, of (3.2 ± 0.3)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+14.080 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.52 (-0.08,+0.09),
the high energy photon index beta = -2.27 (-0.15,+0.11),
the peak energy Ep = 361 (-31,+33) keV,
chi2 = 82/97 dof.

The spectrum near the peak count rate (measured from T0
to T0+4.096 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.40 (-0.11,+0.12),
the high energy photon index beta = -2.39 (-0.24,+0.16),
the peak energy Ep = 384 (-39,+43) keV,
chi2 = 88/95 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB180218_T54845/

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.