GCN Circular 36809

D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

A long-duration GRB 240703A was detected by Konus-Wind (KW)
in the waiting mode at ~00:38:32 UT.
The burst source is located in the northern ecliptic hemisphere.

Corrected for the propagation time, the burst was detected
~2 s before the start time of the fast X-ray transient EP240703a
(T0=T0(EP)=00:38:40 UT; Wang et al., GCN 36807
Loading...
 
 ).
The positional and temporal coincidence of this burst with
the EP transient supports the conclusion that EP240703A
is the GRB counterpart.

A Bayesian block analysis of the KW waiting mode data
in the 20-1250 keV band reveals a >12 sigma count rate
increase in the interval from T0-2 s to T0+136 s.
The burst light curve shows a multi-peaked structure
with the brightest peak around ~T0+13 s.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240703A/

The time-integrated spectrum of the burst, measured from T0-2 s to T0+136 s,
is best described by a power law with exponential cutoff (CPL) model
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.09(-0.30,+0.47) and Ep = 180(-44,+62) keV.

The spectrum near the peak count rate, measured from T0-2 s to T0+33 s,
can be described by a CPL model with
alpha = -0.75(-0.33,+0.41) and Ep = 276(-58,+81) keV.

The total burst fluence is 1.36(-0.18,+0.18)x10^-5 erg/cm^2,
and the 2.944 s peak energy flux, measured from T0+12.5 s,
is 2.8(-0.4,+0.4)x10^-7 erg/cm^2.
(both in the 20 keV - 10 MeV energy range).

All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.