TITLE:   GCN CIRCULAR
NUMBER:  44722
SUBJECT: Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a
DATE:    26/05/28 12:11:41 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 short-duration GRB 260527A
triggered Konus-Wind at T0=22572.142 s UT (06:16:12.142).

The burst light curve shows a multi-peaked structure
which starts at ~T0-0.1 s and has a total duration of ~0.2 s.
The emission is seen up to ~10 MeV.

The burst occurred ~4 min before the Einstein Probe detection of EP260527a (Yang et al., GCN 44718),
and also the KW ecliptic latitude response is consistent with the EP260527a position.
This suggests a common origin of two events, which will be further investigated.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260527_T22572/

As observed by Konus-Wind, the burst
had the total fluence of 1.99(-0.46,+0.57)x10^-6 erg/cm2,
and the 16-ms peak flux, measured from T0-0.008 s,
of 3.09(-1.06,+1.28)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+0.064 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 = -0.67(-0.36,+0.46),
the high energy photon index beta = -2.13(-0.85,+0.36),
the peak energy Ep = 541(-204,+367) keV
(pgstat = 33/45 dof).

A power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.79(-0.42,+0.49)
and Ep = 670(-240,+1097) keV 
fits this spectrum equally well (pgstat = 35/46 dof).

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.