Pulsars, transients and relativistic astrophysics

Abstract:

The Chandra measurement of X-rays from the radio jet in PKS 0637-752 has implications for the source kinematics and energetics. This contribution discusses several possibilities for explaining the high X-ray output from the jet, emphasizing the impact on the assumption of equipartition between relativistic particles and fields in the jet plasma.

Abstract:

We discuss the various contributions to the jet luminosity in proton blazar models of active galactic nuclei and describe a method of estimating the jet luminosity from the observed spectral energy distribution (SED) and the fitted model parameters. We apply this to a synchrotron proton blazar (SPB) model for Markarian 501.

Abstract:

The parsec-scale radio jets of BL Lacertae objects imaged with Very Long Baseline Interferometry (VLBI) show a number of distinctive features. The most striking of these is the dominance of transverse magnetic fields on the wide range of scales probed by VLBI observations at frequencies from 43 to 5 GHz. Some compact VLBI components with transverse fields axe undoubtedly relativistic shocks, in which the transverse field has been enhanced by compression. However, there is considerable evidence that we axe also detecting the toroidal component of an underlying helical magnetic field associated with the VLBI jet.

Abstract:

In February 1997, we obtained multi-frequency polarization VLBA observations of 23 sources from a complete sample of northern BL Lac objects. Total intensity and linear polarization images of two sources (0745+241 and 0820+225) showing evidence for the presence of sheaths of longitudinal magnetic field surrounding their jets are presented. These results suggest that appreciable amounts of thermal plasma are often present on parsec scales, and that the jet magnetic field can be influenced by interaction with this surrounding medium.

Abstract:

FRIIb radio sources axe a special subset of all classical double radio sources with particularly simple radio bridge structures. At low radio frequencies, the surface brightness across the ridge-line of the source is accurately reproduced by accounting for adiabatic expansion in the lateral direction by an amount indicated by the observed change in the width of the radio bridge as a function of position. Thus, the physics of FRIIb sources is quite simple. The radio properties of an FRIIb source may provide a useful probe of the pressure, density, and temperature of gas surrounding the radio source. Estimates of the ambient gas density obtained from considerations of the rain-pressure confinement of the forward region of FRIIb radio sources axe discussed here. Typical ambient gas densities and the composite density profile indicate that the sources lie in gaseous environments very much like the cores of galaxy clusters. Some evolution of the core gas density and radius with redshift axe suggested by the data.