[vsnet-grb-info 24385] Konus-Wind observation of GRB 191213A (ulong)

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26484
SUBJECT: Konus-Wind observation of GRB 191213A (ulong)
DATE:    19/12/18 12:51:10 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova at mail.ioffe.ru>

A. Ridnaia, 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 ultra-long GRB 191213A (Swift-BAT trigger #944091:
Cenko et al., GCN 26398; Lien et al., GCN 26418)
was detected by Konus-Wind (KW) in the waiting mode.

The burst light curve shows the main multipeaked episode of emission
started at ~T0(BAT)-25 s and lasted until ~T0(BAT)+1815 s (the
duration is ~1790 s; T0(BAT)=14781.499 s UT (04:06:21.499)).
There is also a weaker broad pulse of emission seen before the main
pulse from ~T0(BAT)-834 s to ~T0(BAT)-772 s. It might be related to
GRB 191213A (it was detected by the same KW detector, and the KW
ecliptic latitude response for it is consistent with the common
origin with the main episode).

As observed by KW, the burst (main episode) had a fluence of
1.12(-0.06,+0.07)x10^-4 erg/cm2 and a 2.944-s peak flux,
measured from ~T0(BAT)+676.012s, of 2.5(-0.41,+0.41)x10^-7 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The emission shows no signs of strong spectral variability.
Modeling the KW 3-channel time-integrated spectrum
(from ~T0(BAT)-24.660 s to ~T0(BAT)+1815.340 s)
by a power law with exponential cutoff model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.16 (-0.12,+0.14), and Ep = 409 (-71,+110) keV.

Thus, the prompt gamma-ray emission properties of this GRB:
fluence, peak flux, Ep, and duration are similar to those
observed in other ultra-long GRBs.

The KW light curve of this burst is available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB191213A/

All the quoted errors are estimated at the 1 sigma confidence level.
All the presented results are preliminary.