GCN Circular 44474
Subject
Konus-Wind detection of GRB 260504B (short/hard)
Event
Date
2026-05-05T14:25:39Z (4 days ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
Via
email
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 260504B (SVOM/ECLAIRs detection: Saccardi et al., GCN 44454;
SVOM/GRM detection: Wang et al., GCN 44470;
GECAM-B detection: Wang et al., GCN 44473)
triggered Konus-Wind (KW) at T0=34281.198 s UT (09:31:21.198).
The burst light curve shows a single pulse,
which starts at ~T0-0.05 s and has a duration of ~0.21 s.
The emission is seen up to ~6 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260504_T34281/
As observed by Konus-Wind, the burst had the total fluence
of (2.39 ± 0.52)x10^-6 erg/cm^2 and a 16-ms peak energy flux,
measured from T0-0.032, of (2.06 ± 0.45)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 fitted in the 20 keV - 15 MeV range by a power law with exponential
cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.00 (-0.12, + 0.14) and Ep = 1461(-398,+584) keV, chi^2 = 34/32 dof.
Fitting this spectrum by a Band GRB function yields the same values
of alpha and Ep, and only an upper limit on the high energy photon
index beta of -2.1
All the quoted errors are estimated at the 68% confidence level.
All the presented results are preliminary.