The X-ray and radio-emitting plasma lobes of 4C23.56: further evidence
  of recurrent jet activity and high acceleration energies
  New Chandra observations of the giant (0.5 Mpc) radio galaxy 4C23.56 at z =
2.5 show X-rays in a linear structure aligned with its radio emission, but
anti-correlated with the detailed radio structure. Consistent with the
powerful, high-z giant radio galaxies we have studied previously, X-rays seem
to be invariably found where the lobe plasma is oldest even where the radio
emission has long since faded. The hotspot complexes seem to show structures
resembling the double shock structure exhibited by the largest radio quasar
4C74.26, with the X-ray shock again being offset closer to the nucleus than the
radio synchrotron shock. In the current paper, the offsets between these shocks
are even larger at 35kpc. Unusually for a classical double (FRII) radio source,
there is smooth low surface-brightness radio emission associated with the
regions beyond the hotspots (further away from the nucleus than the hotspots
themselves), which seems to be symmetric for the ends of both jets. We consider
possible explanations for this phenomenon, and conclude that it arises from
high-energy electrons, recently accelerated in the nearby radio hotspots that
are leaking into a pre-existing weakly-magnetized plasma that are symmetric
relic lobes fed from a previous episode of jet activity. This contrasts with
other manifestations of previous epochs of jet ejection in various examples of
classical double radio sources namely (1) double-double radio galaxies by e.g.
Schoenmakers et al, (2) the double-double X-ray/radio galaxies by Laskar et al
and (3) the presence of a relic X-ray counter-jet in the prototypical classical
double radio galaxy, Cygnus A by Steenbrugge et al. The occurrence of
multi-episodic jet activity in powerful radio galaxies and quasars indicates
that they may have a longer lasting influence on the on-going structure
formation processes in their environs than previously presumed.
