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GCN Circular 32358

Subject
Konus-Wind detection of GRB 220708B
Date
2022-07-09T16:57:15Z (2 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
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 GRB 220708B (Swift/BAT-GUANO arcminute localization:
Tohuvavohu et al., GCN Circ 32345;
CALET-CGBM detection: Kobayashi et al., GCN Circ 32356)
triggered Konus-Wind (KW) at T0=7620.140 s UT (02:07:00.140).

The burst light curve shows two separated emission episodes.
The first episode (reported in GCNs 32345, 32356)
starts at ~T0-1 s and has a duration of ~4 s.
The second, much longer episode starts at ~T0-380 s and lasts to ~T0+450 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/GRB220708_T07620/

As observed by Konus-Wind, the burst had
a total fluence of (1.23 �� 0.44)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 0.832 s,
of (2.03 �� 0.39)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the first episode (measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.68(-0.22,+0.44) and Ep = 90(-9,+11) keV (chi2 = 77/97 dof).
Fitting this spectrum by a Band function yields the same values of alpha and Ep,
and an upper limit on the high energy photon index beta of -2.8 (chi2 = 76/96 dof).
The fluence in this time interval is (2.8 �� 0.5)E-06 erg/cm^2.

The time-averaged spectrum of the second episode (measured from T0+377.088 to T0+450.816 s)
is best fit in the 20 keV - 15 MeV range by a CPL model
with alpha = -1.48(-0.31,+0.42) and Ep = 146(-45,+66) keV (chi2 = 90/98 dof).
A Band function fits the spectrum equally well with alpha = -1.20 (-0.56,+0.57),
beta = -2.29(-7.71, + 0.34), and Ep = 107 (-32, +68) keV (chi2 = 90/97 dof).
The fluence in this time interval is (9.5 �� 3.9)E-06 erg/cm^2.


All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.
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