TITLE:   GCN CIRCULAR
NUMBER:  14677
SUBJECT: Konus-Wind observation of GRB 130518A
DATE:    13/05/19 13:50:14 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The long-duration intense GRB 130518A
(Fermi-GBM detection: Xiong, GCN 14674;
Fermi-LAT detection: Omodei and Julie McEnery, GCN 14675;
Swift-BAT trigger 556113: Cummings, GCN 14676)
triggered Konus-Wind at T0=50097.501s UT (13:54:57.501)
against very high and variable solar particles background.

The light curve shows a bright hard pulse from ~T0-10 s to ~T0+20s,
followed by a weaker count rate increase at ~T0+33s
and a tail of soft extended emission, which is traceable out to ~T0+100s.

The emission in the main pulse is seen up to 12 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130518_T50097/

As observed by Konus-Wind, the burst
had a fluence of (1.5 ± 0.15)x10-4 erg/cm2,
and a 64-ms peak flux, measured from T0+1.856s,
of (2.1 ± 0.2)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+20.224 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.92 ± 0.08,
the high energy photon index beta = -1.97 ± 0.08,
the peak energy Ep = 370 ± 55 keV,
chi2 = 85/94 dof.

The spectrum at the maximum count rate
(measured from T0+0.768 to T0+2.304 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.80 ± 0.09,
the high energy photon index beta = -2.04 ± 0.11,
the peak energy Ep = 452 ± 72 keV,
chi2 = 95/97 dof.

For both spectra, we note a hint of counts excess
over the model flux in the spectral channels around ~10 MeV.

All the quoted results are preliminary.