Pulsars, transients and relativistic astrophysics

Abstract:

We use numerical simulations to discuss some aspects of the hydrodynamics of radio galaxies, and the affect that hydrodynamical considerations have on the long term evolution of such sources. Using these simulations, we can start to assess the impact that a radio galaxy may have on the energy and entropy budget of its host galaxy or cluster. A full hydrodynamic treatment of radio galaxy expansion is also necessary to interpret correctly the X-ray shells and cavities that, are seen in some sources by ROSAT and Chandra.

Abstract:

The X-ray emission in many clusters of galaxies shows a central peak in surface brightness coincident with a drop in temperature. These characterize a cooling flow. There is also often a radio source at the centre of such a region. Data from Chandra now enable us to map the interaction between the radio source and the intracluster medium. Preliminary work shows no sign of heating of the gas beyond the radio lobes, which are often devoid of cooler gas and so appear as holes. In the case of the Perseus cluster around 3C 84, the coolest X-ray emitting gas occurs immediately around the inner radio lobes.

Abstract:

Optical spectra of the narrow, disturbed, interface regions between radio jets and gas clouds in the interstellar medium of the host galaxies of two nearby radio sources have diagnostic (BPT) diagrams for line ratios of [NII], [OIII], [SII], Halpha and Hbeta which are inconsistent with published models for shock heating, as well as those for photoionization/excitation by either a "hard" continuum or flux from ordinary hot stars. This may indicate the need for additional work on these models or it may indicate that the ionized gas in the jet/cloud interface has an energy distribution which is partly characterised by that in the radio jet plasma itself If the latter is correct, then careful measurements of these interface regions may allow us to distinguish between beams of particles composed of electrons and positrons and those composed of electrons and protons.

Abstract:

The results of a multifrequency VLA imaging study of the nearby radio galaxy 3C 31 are briefly summarized. The transition between jets and lobes is much more complex than was apparent from earlier observations, and is associated with significant variations in spectral index. We demonstrate that the known depolarization asymmetry in 3C 31 is caused by foreground Faraday rotation in the halo of the host galaxy, but the details of the associated field and density structure are not yet clear.