  HESS J1825-137 was detected with a significance of 8.1 $\sigma$ in the
Galactic Plane survey conducted with the H.E.S.S. instrument in 2004. Both HESS
J1825-137 and the X-ray pulsar wind nebula G18.0--0.7 (associated with the
Vela-like pulsar PSR B1823-13) are offset south of the pulsar, which may be the
result of the SNR expanding into an inhomogeneous medium. The TeV size ($\sim
35$ pc, for a distance of 4 kpc) is $\sim 6$ times larger than the X-ray size,
which may be the result of propagation effects as a result of the longer
lifetime of TeV emitting electrons, compared to the relatively short lifetime
of keV synchrotron emitting electrons. The TeV photon spectral index of $\sim
2.4$ can also be related to the extended PWN X-ray synchrotron photon index of
$\sim 2.3$, if this spectrum is dominated by synchrotron cooling. The
anomalously large size of the pulsar wind nebula can be explained if the pulsar
was born with a relatively large initial spindown power and braking index
$n\sim 2$, provided that the SNR expanded into the hot ISM with relatively low
density ($\sim 0.003$ cm$^{-3}$).
