TITLE: GCN CIRCULAR NUMBER: 44677 SUBJECT: Konus-Wind detection of GRB 260519C DATE: 26/05/21 13:10:04 GMT FROM: Dmitry Svinkin at Ioffe Institute <dmitrysvinkin@gmail.com> D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 260519C (NuSTAR-ACS detection: Waratkar et al., GCN 44672) triggered Konus-Wind at T0=49536.443 s UT (13:45:36.443). The burst light curve shows a multipeaked structure which starts at ~T0-3.5 s and has a total duration of ~27 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260519_T49536/ As observed by Konus-Wind, the burst had the total fluence of 2.47(-0.15,+0.13)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+2.192 s, of 2.45(-0.46,+0.46)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+24.832 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 = -0.78(-0.16,+0.18), the high energy photon index beta = -3.17(-0.94,+0.28), the peak energy Ep = 119(-7,+8) keV (chi2 = 96/96 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 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 = -0.70(-0.11,+0.11) and Ep = 209(-10,+11) keV (chi2 = 91/78 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.6 (chi2 = 91/77 dof). 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/44677. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...