GCN Circular 23540

Subject
Konus-Wind observation of GRB 181212A
Event
Date
2018-12-14T11:40:05Z (7 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
D. Frederiks, S. Golenetskii, R.Aptekar, A. Kozlova,
A.Lysenko,  D. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long GRB 181212A (IPN Triangulation: Hurley et al., GCN 23534Loading...
 
 ;
Fermi-GBM detection: Fletcher, GCN 23524Loading...
 
 )
triggered Konus-Wind at T0=59862.922 s UT (16:37:42.922).

The burst light curve shows a single bright pulse followed
by a weaker extended emission.
The total duration of the burst (T90, 80-1300 keV) is ~66 s.
The emission in the main peak is seen up to ~10 MeV.

As observed by Konus-Wind, the burst had a fluence of
(2.4 �� 0.5)x10^-5 erg/cm2 and a 64-ms peak energy flux,
measured from T0+1.536 s, of (1.02 �� 0.13)x10^-5 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+72.448 s)
is best fit in the 20 keV - 15 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -1.75(-0.08,+0.08),
and the peak energy Ep = 216(-45,+84) keV,
chi2 = 100/98 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and only an upper limit on beta (<-2.3).

The spectrum near the peak count rate (measured from T0
to T0+6.912 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 = -1.55 (-0.12,+0.09),
the high energy photon index beta = -2.38 (-7.62,+0.14),
the peak energy Ep = 158 (-20,+47) keV,
chi2 = 101/95 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB181212_T59862/

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.