TITLE: GCN CIRCULAR NUMBER: 35701 SUBJECT: Konus-Wind detection of GRB 240205B (long / very soft) DATE: 24/02/07 17:14:19 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 long GRB 240205B (Fermi GBM observation: Fermi GBM team, GCN 35682; Fletcher et al., GCN 35693; Swift detection: Moss et al., GCN 35683; GECAM detection: Zhang et al., GCN 35689; CALET detection: Sakamoto et al., GCN 35697) triggered Konus-Wind (KW) at T0=79986.680 s UT (22:13:06.680). The burst light curve shows multiple overlapping pulses in the interval from ~T0-5 s to ~T0+57 s, with the brightest peak around ~T0+36 s. The emission is seen up to ~1 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB240205_T79986/ As observed by Konus-Wind, the burst had a total fluence of (3.22 ± 0.18)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0+36.352 s, of (7.38 ± 0.87)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). A time-integrated spectrum (measured from T0 to T0+49.408 s) is best fit in the 20 keV - 1.5 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.80 (-0.08,+0.09), the high energy photon index beta = -3.20 (-6.80,+0.35), the peak energy Ep = 27 (-16,+10) keV, chi2 = 28/49 dof. A spectrum near the peak count rate (measured from T0+33.024 to T0+41.216 s) is best fit in the 20 keV - 15 MeV range by a CPL model with alpha = -1.70(-0.10,+0.11) and Ep = 49(-10,+8) keV (chi2 = 64/62 dof). Fitting this spectrum by a Band function yields the same values of alpha and Ep, and an upper limit on the high energy photon index beta of -3.5 (chi2 = 64/62 dof). Assuming the redshift z=0.824 (Fausey et al., GCN 35698) 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 (6.1 ± 0.3)x10^52 erg, the isotropic peak luminosity L_iso to (2.6 ± 0.5)x10^52 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to ~49 keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to ~89 keV. With the obtained estimates, GRB 240205B is a soft-spectrum outlier in both 'Amati' and 'Yonetoku' relations derived for the sample of >300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB240205_T79986/GRB240205B_rest_frame.pdf All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/35701. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...