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GCN Circular 35140

Konus-Wind detection of GRB 231020A
2023-11-20T19:43:09Z (15 days ago)
Y. Temiraev at Ioffe Institute <>
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Y. Temiraev, D. Svinkin, D. Frederiks, M. Ulanov,
A. Tsvetkova, A. Lysenko, A. Ridnaia, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 231020A
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 34856;
Bala et al., GCN Circ. 34869;
BALROG localization: Preis et al., GCN Circ. 34861;
AstroSat-CZTI detection: Navaneeth et al., GCN Circ. 34880;
GRID detection: Wang and Yang, GCN Circ. 34903;
IPN triangulation: Kozyrev et al., GCN Circ. 34917)
triggered Konus-Wind at T0=68224.628 s UT (18:57:04.628).

The burst light curve shows a single pulse
which starts at ~T0-8.0 s and has a total duration of ~14.2 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
Note: 'dip' in the count rate is due
to the GRB source occultation by the s/c structure.

As observed by Konus-Wind, the burst
had a fluence of 3.37(-0.15,+0.17)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.992 s,
of 1.09(-0.17,+0.17)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+10.240 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.00(-0.12,+0.13),
the high energy photon index beta = -3.11(-0.51,+0.26),
the peak energy Ep = 131(-7,+7) keV
(chi2 = 105/97 dof).

The spectrum near the maximum count rate
(measured from T0 to T0+2.048 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.85(-0.10,+0.11)
and Ep = 185(-9,+10) keV (chi2 = 91/69 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.3
(chi2 = 91/68 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.
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