GCN Circular 16673

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

A long-duration GRB 140808A
(Fermi-GBM detection: Zhang, GCN Circ. 16669
Not found
 
 
)
triggered Konus-Wind at T0=3239.264 s UT (00:53:59.264).

The burst light curve shows two emission episodes, the first,
reported in GCN 16669
Not found
 
 
, from ~T0-1.9 s to ~T0+3.6 s,
and the second, from ~T0+303 s to ~T0+336 s.
The second episode is also seen in the INTEGRAL (SPI-ACS) data but
it can't be unambiguously attributed to the GRB by the triangulation,
so far. The total duration of the burst is ~338 s.

The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB140808_T03239/

As observed by Konus-Wind, the first episode
had a fluence of 3.12(-0.30,+0.33)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0+0.312 s,
of 1.6(-0.4,+0.4)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the first episode
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.95 (-0.26,+0.29)
and Ep = 127 (-18,+25) keV (chi2 = 91/78 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.6
(chi2 = 90/77 dof)

The second episode had a fluence of 4.2(-1.2,+4.0)x10^-6 erg/cm2,
in the 20 keV - 10 MeV energy range.

The time-averaged spectrum of this episode
(measured from T0+303.36 to T0+336.128 s)
is best fit in the 20 keV - 5 MeV range
by the power law with exponential cutoff model
with  alpha = -1.22 (-0.37,+0.48)
and Ep = 376 (-158,+1558) keV (chi2 = 82/88 dof).

Assuming the second episode is related to the GRB the total fluence
is 7.3(-1.2,+4.0)x10^-6 erg/cm2. From the redshift z=3.29
(Gorosabel et al., GCN Circ. 16671
Not found
 
 
)
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.27, and Omega_Lambda = 0.73,
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is ~1.7x10^53 erg,
the peak luminosity L_iso is ~3.8x10^52 erg/s.

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.