A high resolution view of the jet termination shock in a hot spot of the nearby radio galaxy Pictor A: implications for X-ray models of radio galaxy hot spots

摘要

Images made with the VLBA have resolved the region in a nearby radio galaxy,Pictor A, where the relativistic jet that originates at the nucleus terminatesin an interaction with the intergalactic medium, a so-called radio galaxy hotspot. This image provides the highest spatial resolution view of such an objectto date (16 pc), more than three times better than previous VLBI observationsof similar objects. The north-west Pictor A hot spot is resolved into a complexset of compact components, seen to coincide with the bright part of the hotspot imaged at arcsecond-scale resolution with the VLA. In addition to acomparison with VLA data, we compare our VLBA results with data from the HSTand Chandra telescopes, as well as new Spitzer data. The presence of pc-scalecomponents in the hot spot, identifying regions containing strong shocks in thefluid flow, leads us to explore the suggestion that they represent sites ofsynchrotron X-ray production, contributing to the integrated X-ray flux of thehot spot, along with X-rays from synchrotron self-Compton scattering. Thisscenario provides a natural explanation for the radio morphology of the hotspot and its integrated X-ray emission, leading to very different predictionsfor the higher energy X-ray spectrum compared to previous studies. From thesizes of the individual pc-scale components and their angular spread, weestimate that the jet width at the hot spot is in the range 70 - 700 pc, whichis comparable to similar estimates in PKS 2153-69, 3C 205, and 4C 41.17. Thelower limit in this range arises from the suggestion that the jet may dither inits direction as it passes through hot spot backflow material close to the jettermination point, creating a "dentist drill" effect on the inside of a cavity700 pc in diameter.