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GCN Circular 31905

Subject
Konus-Wind detection of GRB 220408B
Date
2022-04-15T18:11:24Z (2 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
A. Lysenko, D. Frederiks, D. Svinkin, M. Ulanov, A. Tsvetkova,
A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, report:

The long-duration GRB 220408B
(Fermi-GBM detection: The Fermi GBM team, GCN Circ. 31854;
AstroSat-CZTI detection: Gopalakrishnan et al., GCN Circ. 31863;
IPN triangulation: Kozyrev et al., GCN Circ. 31878;
Fermi-LAT detection: Bissaldi et al., GCN Circ. 31896;)
triggered Konus-Wind at T0=26885.231 s UT (07:28:05.231).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.5 s and has a total duration of ~35 s.
The emission is seen up to ~3 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB220408_T26885/

As observed by Konus-Wind, the burst
had a fluence of 4.1(-0.4,+0.5)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+3.760 s,
of 7.26(-1.60,+1.63)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+30.976 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 = -0.80(-0.09,+0.11),
the high energy photon index beta = -2.72(-0.54,+0.29),
the peak energy Ep = 231(-20,+20) keV
(chi2 = 84/81 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+6.400 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 = -0.27(-0.16,+0.18),
the high energy photon index beta = -2.39(-0.21,+0.15),
the peak energy Ep = 211(-20,+23) keV
(chi2 = 80/82 dof).

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