TITLE: GCN CIRCULAR NUMBER: 40972 SUBJECT: Konus-Wind detection of short/hard GRB 250704B/ EP250704a DATE: 25/07/05 11:37:01 GMT 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 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/40972. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...