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GCN Circular 31429

Subject
Konus-Wind detection of GRB 220107A
Date
2022-01-10T19:41:10Z (2 years ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 220107A
(Fermi/GBM trigger #663259536: Fermi GBM Team, GCN 31399;
Kunzweiler et al., GCN 31400; Veres and Meegan, GCN 31406;
Swift/BAT-GUANO localization: DeLaunay et al., GCN 31402;
AstroSat CZTI detection: Suresh et al., GCN 31408)
triggered Konus-Wind at T0=53142.427 s UT (14:45:42.427).

The burst light curve shows a multipeaked structure
started at ~T0-7.6 s with a total duration of ~110.8 s.
The emission is seen up to ~2 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB220107_T53142/

As observed by Konus-Wind, the burst
had a fluence of 5.48(-0.30,+0.34)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+81.344 s,
of 8.18(-1.55,+1.54)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+105.984 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.02(-0.11,+0.12)
and Ep = 247(-24,+30) keV (chi2 = 53/61 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.4
(chi2 = 53/60 dof).

The spectrum near the maximum count rate
(measured from T0+73.984 to T0+89.600 s)
is best fit in the 20 keV - 2 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.86(-0.11,+0.12),
the high energy photon index beta = -2.91(-1.53,+0.32),
the peak energy Ep = 186(-15,+17) keV
(chi2 = 46/60 dof).

Assuming the redshift z=1.246 (Castro-Tirado et al., GCN 31423)
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 isotropic energy release E_iso to (2.3 �� 0.1)x10^53 erg,
the isotropic luminosity L_iso to (7.8 �� 1.5)x10^52 erg/s,
the rest-frame peak energy of the time-integrated spectrum Epi,z to (555 ��
67) keV,
and the rest-frame peak energy of the 'peak' spectrum Epp,z to (418 �� 38)
keV.
With these values, GRB 220107A is within 68% prediction bands for
for both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW
GRBs
with known redshifts (Tsvetkova et al., 2021, ApJ, 908, 83),
see http://www.ioffe.ru/LEA/GRBs/GRB220107_T53142/GRB220107A_rest_frame.pdf

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