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GCN Circular 24715

Subject
Konus-Wind observation of extremely bright GRB 190530A
Date
2019-06-02T15:18:51Z (5 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 extremely bright, long GRB 190530A
(Fermi GBM detection: GCN 24676,24692; AGILE-MCAL detection: GCN 24679;
Fermi-LAT detection: GCN 24679; AGILE/GRID analysis: GCN 24683;
AstroSat CZTI detection: GCN 24694) triggered Konus-Wind (KW)
at T0=37146.000 s UT (10:19:06.000).

The light curve of the burst shows a bright, multi-peaked pulse
with a total duration of ~55s, followed by a weaker and softer
emission tail visible until ~T0+150 s.
The emission in the bright phase of the burst is seen up to ~10 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB190530_T37146/

As observed by Konus-Wind, the burst had
a fluence of (5.57 �� 0.15)x10^-4 erg/cm2 and
a 64-ms peak energy flux, measured from T0+14.912,
of (1.59 �� 0.10)x10^-4 erg/cm2 (both in the 20 keV - 10 MeV
energy range).

The time-integrated spectrum (measured from T0 to T0+44.228 s)
is best fit in the 20 keV - 16 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.03 (-0.02,+0.02),
the high energy photon index beta = -3.03 (-0.36,+0.22),
the peak energy Ep = 848 (-33,+44) keV,
chi2 = 140/96 dof.

The spectrum near the peak count rate (measured from T0+14.848 s
to T0+15.104 s) is best fit in the 20 keV - 16 MeV range
by a cutoff power-law (CPL) function with the following model
parameters: the photon index alpha = -0.41(-0.07,+0.07),
and the peak energy Ep = 1176(-46,+47) keV, chi2 = 55/60 dof.
Fitting this spectrum with the GRB (Band) function yields
the same alpha and Ep, and an upper limit on beta of -3.2.

Assuming an upper limit on the burst redshift z<2.2 (Heintz et al.,
GCN 24686) and a standard cosmology with H_0 = 70 km/s/Mpc,
Omega_M = 0.30, and Omega_Lambda = 0.70, we estimate the following
upper limits on the GRB rest-frame energetics: the isotropic energy
release E_iso < 6.4x10^54 erg and the peak luminosity L_iso < 5.8x10^54
erg/s (both in the bolometric 1-10000 keV range).
Location of GRB 190530A in rest-frame hardness-intensity planes,
along with 'Amati' and 'Yonetoku' relations for the KW sample of
GRBs with known redshifts (Tsvetkova et al., ApJ 850 161, 2017), can be
found at http://www.ioffe.ru/LEA/GRBs/GRB190530_T37146/GRB190530A.pdf

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.
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