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GCN Circular 28301

Subject
GRB 200826A: further analysis of the Konus-Wind data and classification
Date
2020-08-28T18:29:11Z (4 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
D. Svinkin, D. Frederiks, A. Ridnaia, and A. Tsvetkova,
on behalf of the Konus-Wind team, report:

Following the X-ray afterglow detection (GCN 28300) and
the identification of possible optical transient (GCN 28295)
spatially coincident with the X-ray source,
we present a further analysis of the KW detection of
the short-duration, soft-spectrum, bright GRB 200826A
(GCNs 28284, 28287, 28288, 28289, 28294).

As observed by KW the burst duration is T50=0.286+/-0.029 s
(T90 = 0.772+/-0.188 s). The position of the GRB 200826A in
the hardness-duration diagram (logT50-logHR32) of 1610 KW bright GRBs
(Svinkin et al., JPhCS 1400, 2, 022010, 2019)
suggests that the burst comes from the long/soft GRB population.
The figure showing the hardness-duration diagram is available at
http://www.ioffe.ru/LEA/GRBs/GRB200826_T16195/GRB200826A_HRT50.png
The contours denote the 1 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=0.7 s marks the boundary used
by Svinkin et al. 2019 to distinguish between short and long KW GRBs.

Assuming the redshift of an underlying galaxy z=0.714 (GCN 28295)
and a standard cosmology model with H_0 = 67.3 km/s/Mpc,
Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is ~4.7x10^51 erg,
the peak luminosity L_iso is ~1.6x10^52 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is ~115 keV.

With these values, GRB 200826A is within the 1 sigma prediction band of
both 'Amati' and 'Yonetoku' relations built for 138 Type II (long/soft) 
GRBs with known z (Tsvetkova et al., ApJ 850 161, 2017).
Meanwile, in both Eiso-Ep,z and Liso-Ep,z planes,
the GRB 200826A position is inconsistent with
short-hard (Type I) GRB population,
see http://www.ioffe.ru/LEA/GRBs/GRB200826_T16195/GRB200826A.pdf

Thus, from the analysis of the KW detection, we conclude, that,
GRB 200826A may be classified as Type II (long/soft, core-collapse origin).
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