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GCN Circular 33827

LIGO/Virgo/KAGRA S230518h: Upper limits from Konus-Wind observations
2023-05-19T16:11:50Z (20 days ago)
Anna Ridnaia at Ioffe Institute <>
A.Ridnaia, D. Frederiks, A.Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: Konus-Wind (KW) was observing the whole sky at the time of the LIGO/Virgo/KAGRA event S230518h (2023-05-18 12:59:08.167 UTC, hereafter T0; LIGO/Virgo/KAGRA Collaboration GCN Circ. 33813, 33816). No triggered or waiting-mode KW GRBs happened between ~10 hours before and ~2 hours after T0 (the current available data). Using waiting-mode data within the interval T0 +/- 100 s, we found no significant (> 5 sigma) excess over the background in both KW detectors on temporal scales from 2.944 s to 100 s. We estimate an upper limit (90% conf.) on the 20 - 1500 keV fluence to 7.6x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having a typical KW short GRB spectrum (an exponentially cut off power law (CPL) with alpha =-0.5 and Ep=500 keV) and to 4.0x10^-7 erg/cm^2 for a burst having spectrum similar to that of GRB 170817A (a CPL with alpha =-0.62 and Ep=185 keV). For a typical long GRB spectrum (the Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the corresponding limiting peak flux is 2.3x10^-7 erg/cm^2/s (20 - 1500 keV, 2.944 s scale). All the quoted values are preliminary.
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