  During our Herschel Lensing Survey (HLS) of massive galaxy clusters, we have
discovered an exceptionally bright source behind the z=0.22 cluster Abell 773,
which appears to be a strongly lensed submillimeter galaxy (SMG) at z=5.2429.
This source is unusual compared to most other lensed sources discovered by
Herschel so far, because of its higher submm flux (\sim 200mJy at 500\micron)
and its high redshift. The dominant lens is a foreground z=0.63 galaxy, not the
cluster itself. The source has a far-infrared (FIR) luminosity of L_FIR= 1.1
10^{14}/\mu Lo, where \mu is the magnification factor, likely \sim 11. We
report here the redshift identification through CO lines with the IRAM-30m, and
the analysis of the gas excitation, based on CO(7-6), CO(6-5), CO(5-4) detected
at IRAM and the CO(2-1) at the EVLA. All lines decompose into a wide and strong
red component, and a narrower and weaker blue component, 540\kms apart.
Assuming the ultraluminous galaxy (ULIRG) CO-to-H2 conversion ratio, the H2
mass is 5.8 10^{11}/\mu Mo, of which one third is in a cool component. From the
CI line we derive a CI/H2 number abundance of 6 10^{-5} similar to that in
other ULIRGs. The H2O line is strong only in the red velocity component, with
an intensity ratio I(H_2O)/I(CO) \sim 0.5, suggesting a strong local FIR
radiation field, possibly from an active nucleus (AGN) component. We detect the
[NII]205\mics line for the first time at high-z. It shows comparable blue and
red components, with a strikingly broad blue one, suggesting strong ionized gas
flows.
