[vsnet-grb-info 17728] Konus-Wind observation of GRB 160310A (possible ultra-long GRB?)

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19167
SUBJECT: Konus-Wind observation of GRB 160310A (possible ultra-long GRB?)
DATE:    16/03/11 17:33:47 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 160310A (Fermi/LAT detection: Vianello et al., GCN 19158;
Fermi/GBM detection: Toelge & Hui, GCN 19161)
triggered Konus-Wind at T0=1391.997 s UT (00:23:11.997).

The light curve shows a multi-peaked pulse which started
at ~T0-14 s and lasted until ~T0+15 s (the total duration is ~30 s).
The emission is seen up to ~4 MeV.

As observed by Konus-Wind, the burst had a fluence of
(6.8 ± 1.5)x10^-6 erg/cm2 and a 64-ms peak energy flux,
measured from T0-0.192, of (2.1 ± 0.4)x10^-6 erg/cm2
(both in the 20 keV - 10 MeV energy range).

The spectrum of the burst (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range by a cutoff power-law
(CPL) function with the following model parameters:
the photon index alpha = -1.40(-0.16,+0.21),
and the peak energy Ep = 316(-95,+206) keV,
chi2 = 89/85 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep with only an upper limit on beta of -2.0,
chi2 = 89/94 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB160310_T01391/

In the KW waiting mode data, GRB 160310A was preceded by
a weaker, GRB-like event lasting from ~T0-1510 s to ~T0-1418 s
(the total duration is ~90 s).
Modeling the KW 3-channel spectrum for this episode
by the CPL function yields alpha = -1.23 ± 0.24, Ep = 142 ± 57 keV,
and a 20--1500 keV fluence of (7.7 ± 1.7)x10^-6 erg/cm2.
The KW ecliptic latitude response for this event is consistent
with that for GRB 160310A. Taking this into account,
we suggest a possibility that GRB 160310A is, in fact,
a double-episode, ultra-long GRB with a total duration of ~1500 s.

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