Konus-Wind detection of GRB 210204A / ZTF21aagwbjr

The long GRB 210204A (Fermi GBM detection: Bissaldi, GCN 29393; GECAM detection: Li et al, GCN 29392; IPN triangulation: Hurley et al., GCN 24908; AstroSat CZTI Detection: Waratkar et al., GCN 29410), associated with the fast optical transient ZTF21aagwbjr/AT2021buv (Kool et al., GCN 29405), triggered Konus-Wind (KW) at T0=23570.576 s UT (06:32:50.576). The burst light shows a bright, multi-peaked pulse, which starts at ~T0-30 s and has a duration of ~80 s. A weaker precursor is clearly visible in the KW waiting mode data around ~T0-165 s. The emission in the main pulse is seen up to ~3 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/ As observed by Konus-Wind, the burst had a fluence of (5.7 ± 0.9)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0+2.304, of (5.0 ± 0.7)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+49.408 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.04 (-0.12,+0.18), the high energy photon index beta = -2.43 (-0.18,+0.31), the peak energy Ep = 137 (-25,+22) keV, chi2 = 79/97 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.28 (-0.54,+0.64), the high energy photon index beta = -2.12 (-0.24,+0.11), the peak energy Ep = 123 (-24,+49) keV, chi2 = 109/97 dof. Assuming the redshift z=1.466 (Izzo et al., GCN 29411) 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 isotropic energy release E_iso to ~2.3x10^53 erg, the isotropic luminosity L_iso to ~7.1x10^52 erg/s, and the rest-frame peak energy of the time-integrated spectrum Ep,z to ~340 keV. With these values, GRB 210204A is within 68% prediction bands for both 'Amati' and 'Yonetoku' relations for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., ApJ, in press), see http://www.ioffe.ru/LEA/GRBs/GRB210204_T23570/GRB210204A_rest_frame.pdf All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.