[vsnet-grb-info 17040] GRB 150906B: Further analysis of the Konus-Wind data

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18321
SUBJECT: GRB 150906B: Further analysis of the Konus-Wind data
DATE:    15/09/16 13:33:08 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin at mail.ioffe.ru>

D. Svinkin, D. Frederiks, and V. Pal'shin,
on behalf of the Konus-Wind team, report:

It was suggested by Levan et. al. (GCN 18263) that the short-duration,
hard-spectrum, bright GRB 150906B (Golenetskii et al. GCN 18259) might
be connected with the NGC 3313 galaxy group. Continuing the discussion
on the possible origin of GRB 150906B (Ruffini et al. GCN 18296 and
F. Zhang et al. GCN 18298) we present a further analysis of the KW data
for this GRB.

Among ~300 bursts from the Konus catalog of short GRBs
(Svinkin et al., in preparation), GRB 150906B is within top 25%
in the terms of 16-ms peak energy flux and within top 3% in the terms
of the total energy fluence, both in the 20 keV - 10 MeV range.
In the terms of Epeak (CPL model), the burst is within 25% hardest
GRBs in the sample.

However, the burst duration is rather long T50=0.952+/-0.036 s
(T90 = 1.642+/-0.076 s). The position of the GRB 150906B in
the hardness-duration diagram (logT50-logHR32) of 1143 KW bright GRBs
cannot exclude that the burst comes from the long GRB population.
The figure showing the hardness-duration diagram is available at
http://www.ioffe.ru/LEA/GRBs/GRB150906_T31340/GRB150906B_T50HR.png
The contours denote the 1, 2, and 3 sigma confidence regions for
two-dimensional Gaussian distributions. The HR32 is the ratio of counts
in the 200-760 keV and 50-200 keV bands accumulated during burst
duration. The vertical dashed line at T50=0.6 s marks the boundary used
by Svinkin et al. to distinguish between short and long KW GRBs.

The spectral lag calculated between the KW 400-1500 keV and 25-100 keV
band light curves (tau = 70+/-40 ms, 68% confidence level)
is consistent, within 68% CL, with the KW lag distributions
for both short and long GRBs.

Thus, being hard enough, GRB 150906B cannot be unambiguously
classified as a short/hard from the KW data.