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GCN Circular 32295

Subject
Konus-Wind detection of GRB 220627A
Date
2022-06-29T17:44:21Z (2 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova,
M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:

The ultra-long (or possible lensed) GRB 220627A
(Fermi-GBM detection: Roberts et al., GCN 32288;
Fermi-LAT detection: Di Lalla et al., GCN 32283;
Swift/BAT-GUANO detection: Raman et al., GCN 32287)
was detected by Konus-Wind (KW) in the waiting mode.

A Bayesian analysis of the burst light curve (lc) reveals
two separated, multi-peaked emission episodes.
The first episode starts at ~T0-140 s and ends at ~T0+290 s;
the second, weaker episode starts at ~T0+915 s and ends at ~T0+1150 s;
where T0 = T0(GBM) = 21:21:00 UT.

Although the described structure of the burst lc is consistent with that reported by GBM (GCN 32288),
a weak emission tail that can be traced in the KW soft energy band (~20-100 keV) till ~T0+3700 s.
We note that this extended emission is visible in the same KW detector,
i.e., it came from the same (southern) ecliptic hemisphere,
however its attribution to GRB 220627A cannot be unambiguously confirmed from the KW data alone.

The KW light curve of this burst is available
at http://www.ioffe.ru/LEA/GRBs/GRB220627A/

Modeling a time-integrated spectrum of the burst (measured from T0-140 s to T0+1150 s)
by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
yields alpha = -1.23 (-0.14, + 0.19) and Ep = 250 (-49,+60) keV.
In the 10 keV -10 MeV band, standard for the KW analysis,
the total burst fluence is (1.07 �� 0.12)x10^-4 erg/cm^2
and the 2.944 s peak energy flux is (9.7 �� 0.7)x10^-7 erg/cm^2/s.

The spectrum of the first episode alone can be described by a CPL
with alpha = -0.85 (-0.09, + 0.09) and Ep = 324 (-19,+21) keV;
and the spectrum of the second, weaker episode -  by a CPL
with alpha = -1.61 (-0.11, + 0.14) and Ep = 301 (-87,+233) keV.
 From these fits, fluences in two individual episodes
are estimated to (7.2 �� 0.7)x10^-5 erg/cm^2 and (3.2 �� 1.2)x10^-5 erg/cm^2, respectively.

Assuming the redshift z=3.084 (Izzo et al., GCN 32291)
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 (2.3 �� 0.3)x10^54 erg,
the isotropic peak luminosity L_iso on the (1+z)*64ms scale to (1.3 �� 0.1)x10^53 erg/s,
and the rest-frame peak energy of the time-integrated spectrum Ep,z to 1020(-200,+250) keV.
With the obtained estimates, GRB 220627A is inside 68% prediction bands
for both 'Amati' and 'Yonetoku' relations 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/GRB220627A/GRB220627A_rest_frame.pdf
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