TITLE:   GCN CIRCULAR
NUMBER:  33827
SUBJECT: LIGO/Virgo/KAGRA S230518h: Upper limits from Konus-Wind observations
DATE:    23/05/19 16:11:50 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:

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.