Extended X-ray emission in PKS 1718$-$649
  PKS 1718$-$649 is one of the closest and most comprehensively studied
candidates of a young active galactic nucleus (AGN) that is still embedded in
its optical host galaxy. The compact radio structure, with a maximal extent of
a few parsecs, makes it a member of the group of compact symmetric objects
(CSO). Its environment imposes a turnover of the radio synchrotron spectrum
towards lower frequencies, also classifying PKS 1718$-$649 as gigahertz-peaked
radio spectrum (GPS) source. Its close proximity has allowed the first
detection of extended X-ray emission in a GPS/CSO source with Chandra that is
for the most part unrelated to nuclear feedback. However, not much is known
about the nature of this emission. By co-adding all archival Chandra data and
complementing these datasets with the large effective area of XMM-Newton, we
are able to study the detailed physics of the environment of PKS 1718$-$649.
Not only can we confirm that the bulk of the $\lesssim$kiloparsec-scale
environment emits in the soft X-rays, but we also identify the emitting gas to
form a hot, collisionally ionized medium. While the feedback of the central AGN
still seems to be constrained to the inner few parsecs, we argue that
supernovae are capable of producing the observed large-scale X-ray emission at
a rate inferred from its estimated star formation rate.
