The X-ray and radio-emitting plasma lobes of 4C23.56: further evidence of recurrent jet activity and high acceleration energies

• Published in: Monthly notices of the Royal Astronomical Society 2011-04, Vol.412 (2), p.705-710
• Main Authors: Blundell, Katherine M., Fabian, A. C.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; galaxies: high-redshift; galaxies: jets; Plasma; Radio astronomy; Star & galaxy formation; Stars & galaxies; X-ray astronomy; X-rays: individual: 4C23.56
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2010.17608.x

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 seemingly anticorrelated 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 ∼35 kpc. Unusually for a classical double (FR II) radio source, there is smooth low surface-brightness radio emission associated with the regions beyond the hotspots (i.e. 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 reach the conclusion 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 (i) double-double radio galaxies by e.g. Schoenmakers et al., (ii) the double-double X-ray/radio galaxies by Laskar et al. and (iii) the presence of a relic X-ray counter-jet in the prototypical classical double radio galaxy, Cygnus A by Steenbrugge et al. The occurrence, still more the prevalence, of multi-episodic jet activity in powerful radio galaxies and quasars indicates that they may have a longer lasting influence on the ongoing structure formation processes in their environs than previously presumed.