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GCN Circular 22609

Subject
Konus-Wind observation of GRB 180404B
Date
2018-04-06T13:33:29Z (6 years ago)
From
Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>
D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks,
M. Ulanov, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 180404B
(Swift-BAT detection: LaPorte et al., GCN Circ. 22590;
Fermi-GBM observation: von Kienlin, GCN Circ. 22597)
triggered Konus-Wind at T0=7898.049 s UT (02:11:38.049).

The burst light curve shows the bright pulse
which starts at ~T0-3.4 s and has a total duration of ~29 s
followed by a weaker pulse seen up to ~T0+100 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/GRB180404_T07898/

As observed by Konus-Wind, the burst
had a fluence of 2.60(-0.16,+0.18)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+8.832 s,
of 2.07(-0.66,+0.66)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+73.984 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.65(-0.15,+0.16)
and Ep = 205(-17,+21) keV (chi2 = 82/73 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.0
(chi2 = 82/72 dof).

The spectrum near the maximum count rate
(measured from T0+8.448 to T0+16.640 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
with  alpha = -0.19(-0.16,+0.17)
and Ep = 186(-11,+12) keV (chi2 = 90/73 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.2
(chi2 = 90/72 dof).

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