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GCN Circular 35377

Subject
Konus-Wind detection of GRB 231215A
Date
2023-12-16T18:27:11Z (2 months ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
legacy email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long, bright GRB 231215A (Swift detection: D'Avanzo et al., GCN 35343;
AstroSat CZTI detection: Navaneeth et al., GCN 35352;
CALET Gamma-Ray Burst Monitor detection: Cannady et al., GCN 35368;
AGILE detection: Verrecchia et al., GCN 35361;
Fermi GBM detection: Lesage et al., GCN 35369)
triggered Konus-Wind (KW) at T0=35239.795 s UT (09:47:19.795).

The burst light curve shows a single multi-peaked pulse,
which starts at ~T0-1 s, peaks at ~T0+9.5 s,
and has a total duration of ~25 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB231215_T35239/

As observed by Konus-Wind, the burst had
a fluence of (1.02 ± 0.09)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 28.352 s,
of (1.14 ± 0.12)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+24.320 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.67 (-0.07,+0.08),
the high energy photon index beta = -2.49 (-0.43,+0.22),
the peak energy Ep = 612 (-63,+74) keV,
chi2 = 80/97 dof.

The spectrum near the peak count rate (measured from T0+6.400s to T0+9.984s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.49 (-0.09,+0.09),
the high energy photon index beta = -3.07 (-2.04,+0.44),
the peak energy Ep = 582 (-54,+58) keV,
chi2 = 69/80 dof.

Assuming the redshift z=2.305 (Thoene et al., GCN 35373)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the burst isotropic energy release E_iso to (1.35 ± 0.12)x10^54 erg,
the isotropic peak luminosity L_iso to (4.93 ± 0.49)x10^53 erg/s,
the rest-frame peak energy of the time-integrated spectrum Ep,i,z to ~2023 keV,
and the rest-frame peak energy at the peak of the emission Ep,p,z to ~1924 keV.
With the obtained estimates, GRB 230818A is inside 68% prediction band for
both 'Amati' and 'Yonetoku' relations derived for the sample of >300 long
KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB231215_T35239/GRB231215A_rest_frame.pdf

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.


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