Dying and relic radio galaxies: vibrant in X-rays

If radio galaxies have a finite lifetime, then there should exist dying or relicexamples i.e. radio galaxies whose central engines have ceased to be active butwhose extended lobes have not yet faded from view. But only a very few are knownat radio wavelengths: they are so rare because the relic stage is veryshortlived for a radio galaxy whose lobes are no longer continuously injectedwith freshly accelerated particles from the hotspots. Though relic radiogalaxies are very rare, they represent an unexplored phase in the lifecycle ofradio galaxies: as radio galaxies die, their relativistic particles lose energybut dramatically increase the population of Lorentz factor 1000 particles which,importantly, inverseCompton upscatter CMB photons to the Xray band. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]