GCN Circular 32152
Subject
Konus-Wind observation of GRB 220527A
Event
Date
2022-05-30T16:59:09Z (3 years ago)
From
Alexandra Lysenko at Ioffe Institute <alexandra.lysenko@mail.ioffe.ru>
A. Lysenko, D. Frederiks, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov,
and T. Cline on behalf of the Konus-Wind team, report:
The long-duration GRB 220527A
(AGILE detection: Ursi et al., GCN Circ. 32129;
Fermi-LAT detection: Bissaldi et al., GCN Circ. 32131;
Fermi-GBM detection: The Fermi GBM team, GCN Circ. 32130;
Mangan et al., GCN Circ. 32133;
CALET detection: Yamaoka et al., GCN Circ. 32139;
AstroSat CZTI detection: Gopalakrishnan et al., GCN Circ. 32140)
triggered Konus-Wind at T0=33441.517 s UT (09:17:21.517).
The burst light curve shows a multipeaked structure
which starts at ~T0-4.1 s and has a total duration of ~21.3 s.
The emission is seen up to ~16 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB220527_T33441/
As observed by Konus-Wind, the burst
had a fluence of 5.98(-0.31,+0.32)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+5.152s,
of 1.73(-0.21,+0.22)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+13.568 s)
is best fit in the 20 keV - 16 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.80(-0.12,+0.13),
the high energy photon index beta = -2.55(-0.13,+0.10),
the peak energy Ep = 154(-10,+10) keV
(chi2 = 115/98 dof).
The spectrum near the maximum count rate
(measured from T0+3.584 to T0+5.376 s)
is best fit in the 20 keV - 16 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.49(-0.18,+0.21),
the high energy photon index beta = -3.24(-0.53,+0.31),
the peak energy Ep = 146(-9,+9) keV
(chi2 = 72/64 dof).
For both spectra, we note a prominent count excess over the model
at energies above ~5 MeV. The excess can be modeled by
an additional power-law component with a photon index of <~2.
Assuming the redshift z=0.857 (Xu et al., GCN Circ. 32141)
and a standard cosmology model with H_0 = 67.7 km/s/Mpc,
Omega_M = 0.310, and Omega_Lambda = 0.689 (Planck Collab 2018, Paper VI),
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is 1.22(-0.06,+0.07)x10^53 erg,
the peak luminosity L_iso is 6.53(-0.81,+0.84)x10^52 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i,z is 286(-18,+19) keV
With the obtained estimates, GRB 220527A lies 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/GRB220527_T33441/GRB220527A_rest_frame.pdf
All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.