TITLE:   GCN CIRCULAR
NUMBER:  40512
SUBJECT: Konus-Wind detection of GRB 250520A (short/hard)
DATE:    25/05/21 14:42:50 GMT
FROM:    Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>

D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The short GRB 250520A (Swift detection: Eyles-Ferris et al., GCN 40491;
SVOM/GRM observation: Wang et al., GCN 40495; AstroSat CZTI detection:
Tembhurnikar et al., GCN 40497)
triggered Konus-Wind (KW) at T0=9741.866 s UT (02:42:21.866).

The burst light curve shows a single pulse,
which starts at ~T0-0.07 s and has a duration of ~0.26 s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250520_T09741/

As observed by Konus-Wind, the burst had the total fluence
of (3.38 ± 0.75)x10^-6 erg/cm^2 and a 16-ms peak energy flux,
measured from T0-0.032, of (3.49 ± 0.81)x10^-5 erg/cm^2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst (measured from T0 to T0+0.192 s)
is best fit in the 20 keV - 15 MeV range by a GRB (Band) function
with the following model parameters:
the low-energy photon index alpha = -0.48 (-0.27,+0.41),
the high energy photon index beta = -2.51 (-1.99,+0.47),
the peak energy Ep = 671 (-211,+247) keV,
chi2 = 37/27 dof.

The spectrum near the peak count rate (measured from T0 to T0+0.064 s)
is best fit in the 20 keV - 15 MeV range by a GRB (Band) function
with the following model parameters:
the low-energy photon index alpha = -0.67 (-0.27,+0.46),
the high energy photon index beta = -2.39 (-7.61,+0.53),
the peak energy Ep = 1099 (-505,+876) keV,
chi2 = 11/17 dof.


All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.