Pulsars, transients and relativistic astrophysics

Abstract:

The shapes of synchrotron spectra contain important information about the origin and evolution of the relativistic electron distributions. The analyses of spectral shapes that appear in the literature are inadequate, at best, to address the important scientific issues. A proper analysis of spectra can illuminate the energy distribution of particles as they are "injected" into diffuse regions, the acceleration and loss processes, the bulk and microscopic transport of electrons and the role of inhomogeneities in the magnetic field. I describe some observational difficulties we face in isolating the actual particle distributions, highlight some of the interpretational "sins" we have committed, and make some modest recommendations.

Abstract:

We are investigating possible triggering scenarios which may give rise to powerful jetted active galaxies such as classical double radio galaxies. Important clues come from studying those objects which have most recently been triggered. The newly discovered 'Youth-Redshift Degeneracy' for classical double radio galaxies means that the highest redshift objects in a flux-limited survey will be observed to be significantly younger (more recently triggered) than the more nearby objects. We are pursuing this investigation with a new sample specially filtered to favour the detection of high-redshift radio galaxies. We will present some preliminary results of a near-IR imaging campaign using the UIFTI on the UKIRT.

Abstract:

We review several ways in which X-ray observations are helping to tie down the physical parameters in radio lobes and jets, resolving most of the notorious uncertainties which afflict estimates from synchrotron emission alone. Together, the new results imply that the energy density of jet plasma is dominated by particles which do not contribute to the observed radiation, such as relativistic protons or mildly relativistic electrons, These components have long been hypothesised but their implications have often been ignored. Their presence substantially increases estimates of the energy budget for jet activity, and implies that jets may be an important heat source for the intracluster gas.

Abstract:

We discuss prospects for cluster detection via the Sunyaev-Zel'dovich (SZ) effect in a blank field survey with the interferometer array, the Arcminute MicroKelvin Imager (AMI). Clusters of galaxies selected in the SZ effect probe cosmology and structure formation with little observational bias, because the effect measures integrated gas pressure directly, and does so independently of cluster redshift. We use hydrodynamical simulations in combination with the Press-Schechter expression to simulate SZ cluster sky maps. These are used with simulations of the observation process to gauge the expected SZ cluster counts. Even with a very conservative choice of parameters we find that AMI will discover at least several tens of clusters every year with Mtot ≥ 1014M⊙; the numbers depend on factors such as the mean matter density, the density fluctuation power spectrum and cluster gas evolution. The AMI survey itself can distinguish between these to some degree, and parameter degeneracies are largely eliminated given optical and X-ray follow-up of these clusters; this will also permit direct investigation of cluster physics and what drives the evolution.