TITLE: GCN CIRCULAR NUMBER: 44597 SUBJECT: Konus-Wind detection of GRB 260511B DATE: 26/05/13 12:12:06 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 260511B (Fermi-GBM detection: Fermi GBM team, GCN 44542; Roberts et al., GCN 44554; SVOM detection: Godet et al., GCN 44543; NuSTAR detection: Waratkar & Grefenstette, GCN 44556; AstroSat-CZTI detection: Arya et al., GCN 44560) triggered Konus-Wind at T0=39635.267 s UT (11:00:35.267). The burst light curve shows two separate multipeaked episodes: the first from ~T0-1.1 s to ~T0+10 s, and the second, which is brighter and spectrally harder, from ~T0+26 s to ~T0+42 s. The total duration of the burst is ~43.4 s. The burst light curve shows two multipeaked episodes started at ~T0-1.1 s with a total duration of ~43.4 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260511_T39635/ As observed by Konus-Wind, the burst had a fluence of 2.48(-0.11,+0.12)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+30.512 s, of 6.82(-0.83,+0.84)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.12(-0.09,+0.10) and Ep = 259(-20,+24) keV (chi2 = 92/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.4 (chi2 = 92/98 dof). The spectrum near the maximum count rate (measured from T0+24.832 to T0+33.024 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.87(-0.23,+0.17), the high energy photon index beta = -2.26(-0.66,+0.13), the peak energy Ep = 273(-40,+102) keV (chi2 = 93/81 dof). Assuming the redshift z=2.006 (de Ugarte Postigo et al., GCN 44565; Wang et al., GCN 44571) and a standard cosmology model with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is 2.53(-0.11,+0.12)x10^53 erg, the peak luminosity L_iso is 2.09(-0.25,+0.26)x10^53 erg/s, the rest-frame peak energy of the time-averaged spectrum, Ep,i,z is 778(-60,+72) keV and the spectrum near the maximum count rate Ep,p,z is 821(-120,+307) keV. With the obtained estimates, GRB 260511B is inside 68% prediction bands for both the 'Amati' and the '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/GRB260511_T39635/GRB260511B_rest_frame.pdf All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/44597. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...