  Energetic pulsars can be embedded in a nebula of relativistic leptons which
is powered by the dissipation of the rotational energy of the pulsar. The
object PSR J0855-4644 is an energetic and fast-spinning pulsar (Edot =
1.1x10^36 erg/s, P=65 ms) discovered near the South-East rim of the supernova
remnant (SNR) RX J0852.0-4622 (aka Vela Jr) by the Parkes multibeam survey. The
position of the pulsar is in spatial coincidence with an enhancement in X-rays
and TeV gamma-rays, which could be due to its putative pulsar wind nebula
(PWN).
  The purpose of this study is to search for diffuse non-thermal X-ray emission
around PSR J0855-4644 to test for the presence of a PWN and to estimate the
distance to the pulsar. An X-ray observation was carried out with the
XMM-Newton satellite to constrain the properties of the pulsar and its nebula.
The absorption column density derived in X-rays from the pulsar and from
different regions of the rim of the SNR was compared with the absorption
derived from the atomic (HI) and molecular (12CO) gas distribution along the
corresponding lines of sight to estimate the distance of the pulsar and of the
SNR.
  The observation has revealed the X-ray counterpart of the pulsar together
with surrounding extended emission thus confirming the existence of a PWN. The
comparison of column densities provided an upper limit to the distance of the
pulsar PSR J0855-4644 and the SNR RX J0852.0-4622 (d<900 pc). Although both
objects are at compatible distances, we rule out that the pulsar and the SNR
are associated. With this revised distance, PSR J0855-4644 is the second most
energetic pulsar, after the Vela pulsar, within a radius of 1 kpc and could
therefore contribute to the local cosmic-ray e-/e+ spectrum.
