GCN Circular 40972
Subject
Konus-Wind detection of short/hard GRB 250704B/ EP250704a
Event
Date
2025-07-05T11:37:01Z (19 hours ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The short-duration GRB 250704B
(SVOM/GRM observation: Wang et al. GCN 40940;)
associated with the EP X-ray transient EP250704a
(Li et al. GCN 40491, 40956) triggered Konus-Wind (KW)
at T0=29791.045 s UT (08:16:31.045).
The burst shows multiple emission pulses and has a total duration of ~0.4 s.
The emission is seen up to ~8 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250704_T29791/
As observed by Konus-Wind, the burst had
a fluence of (4.24 ± 0.65)x10^-6 erg/cm^2 and
a 16-ms peak energy flux, measured from T0 + 0.240 s,
of (5.82 ± 0.89)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum (measured from T0 to T0+0.256 s)
is best fit in the 20 keV - 15 MeV range by a GRB (Band) function
with the following model parameters:
the low-energy photon index alpha = -1.17 (-0.08,+0.09),
the high energy photon index beta = -2.48 (-1.91,+0.39),
the peak energy Ep = 935(-197,+305) keV,
chi2 = 53/44 dof.
Assuming the redshift z=0.661 (An et al., GCN 40966)
and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
and Omega_Lambda = 0.685 (Planck Collaboration, 2014),
we estimate the burst isotropic energy release E_iso to (5.15 ± 0.79)x10^51 erg,
the isotropic peak luminosity L_iso to (1.17 ± 0.18)x10^53 erg/s, and
the rest-frame peak spectral energy Ep,z to 1550(-330,+510) keV.
With the obtained estimates, the position of GRB 250704B
is consistent with Type I (short/hard) GRB population in both 'Amati' and 'Yonetoku'
diagrams for the sample of KW GRBs with known redshifts
(Tsvetkova et al., 2017; Tsvetkova et al., 2021),
see http://www.ioffe.ru/LEA/GRBs/GRB250704_T29791/GRB250704B_rest_frame.pdf
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.