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GCN Circular 36028

Subject
Konus-Wind detection of LXT 240402A/GRB 240402B
Date
2024-04-04T15:59:11Z (16 days ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 240402B 
(GECAM-C detection: Xue et al., GCN 36017)
associated with the LEIA fast X-ray transient 
LXT 240402A (Xu et al., GCN 36016)
triggered Konus-Wind at T0=31668.797 s UT (08:47:48.797).

The burst light curve shows a multipeaked structure
which starts at ~T0-0.2 s and has a total duration of ~5.1 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/GRB240402_T31668/

As observed by Konus-Wind, the burst
had a fluence of 7.56(-0.43,+0.50)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+2.704 s,
of 5.07(-0.66,+0.68)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+8.448 s)
is best fit in the 20 keV - 4 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.71(-0.17,+0.19),
the high energy photon index beta = -3.58(-1.30,+0.44),
the peak energy Ep = 86(-4,+5) keV
(chi2 = 57/68 dof).

This spectrum is nearly-well fitted 
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.78(-0.15,+0.16)
and Ep = 88(-4,+4) keV (chi2 = 61/69 dof).

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

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