Chandra observation of Cepheus A: The diffuse emission of HH 168
  resolved
  X-ray emission from massive stellar outflows has been detected in several
cases. We present a Chandra observation of HH 168 and show that the soft X-ray
emission from a plasma of 0.55 keV within HH 168 is diffuse. The X-ray emission
is observed on two different scales: Three individual, yet extended, regions
are embedded within a complex of low X-ray surface brightness. Compared to the
bow shock the emission is displaced against the outflow direction. We show that
there is no significant contribution from young stellar objects (YSOs) and
discuss several shock scenarios that can produce the observed signatures. We
establish that the X-ray emission of HH 168 is excited by internal shocks in
contrast to simple models, which expect the bow shock to be the most X-ray
luminous.
