GCN Circular 14368

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 GRB 130408A
(Swift/BAT trigger=553132: Lien et al., GCN 14361
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 )
triggered Konus-Wind at T0=78701.184s UT (21:51:41.194)

The light curve shows a bright pulse from ~T0-0.5 to ~T0+5 s
followed by a much weaker emission pulse peaked around ~T0+12;
a total duration of the burst is ~15 s.
The emission is seen up to several MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130408_T78701/

As observed by Konus-Wind, the burst
had a fluence of (1.2 � 0.2)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+3.328s,
of (5.2 � 0.5)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+16.640 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 = -0.4 � 0.2,
the high energy photon index beta = -2.3 � 0.2,
the peak energy Ep = 211 � 29 keV,
chi2 = 99.4/97 dof.

The spectrum at the maximum count rate (measured from T0 to T0+8.448 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 = -0.70 � 0.15,
the high energy photon index beta = -2.3 � 0.3,
the peak energy Ep = 272 � 40 keV,
chi2 = 87.7/99 dof.

Assuming redshift z=3.758 (Hjorth et al., GCN 14365
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 ; Tanvir et al., GCN 14366
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 ),
and a standard cosmology (H_0=70 km/s/Mpc, Omega_M=0.3, Omega_\Lambda=0.7),
we estimate the following cosmological rest-frame parameters of the prompt
gamma-ray emission:
- the isotropic equivalent energy release E_iso = (3.3 � 0.6)x10^53 erg;
- the peak luminosity L_iso = (5.5 � 0.5)x10^53 erg/s;
- the peak energy of the time-integrated spectrum Ep_rest = 1.00 � 0.14 MeV.

All the quoted results are preliminary.