Pulsars, transients and relativistic astrophysics

Abstract:

We review recent observations of circularly polarized radiation from AGN made with the VLBA and with the ATCA. We also discuss briefly the detections of the Galactic sources Sgr A* and SS 433. The origin of the circular polarization is still an open question in most cases, and we discuss four possible mechanisms. Detectable circular polarization is a common property of quasars, but not of radio galaxies, and is always associated with the compact core. There is growing evidence that the sign of the circular polarization stays the same over at least 20 - 30 years, suggesting that it is a fundamental property of the jet.

Abstract:

The observational picture for cosmic rays above 10(19) eV is described and the enigma that these results pose is discussed. The existence of particles above 10(20) eV may have an impact on our understanding of magnetic fields in intergalactic space and in possible sources.

Abstract:

A majority of a complete sample of 3CR FR I radio galaxies show unresolved optical nuclear sources on the scales of 0.1 aresec. About half of the 3CR FR II radio galaxies observed with the HST also show Compact Central Cores (CCC). These CCCs have been interpreted as the optical counterparts of the non-thermal radio cores in these radio galaxies (Chiaberge, Capetti & Celotti 1999). We show that the optical flux density of the CCCs in FR Is is correlated with the radio core prominence. This correlation supports the argument of Chiaberge et al. that the CCC radiation is of a non-thermal synchrotron origin, which is relativistically beamed along with the radio emission.

Abstract:

We present the results of a year-long WSRT monitoring campaign for the quasar J 1819+3845. The extreme variations (regularly 10% per minute) axe explained by interstellar scintillation of a source which is no more that 30 microarrseconds in diameter, with a corresponding brightness temperature of similar to 10(13) K.We use the results of this WSRT campaign to infer critical source parameters (size, structure and lifetime). To first order, the changes in the observed scintillation behaviour over the year are interpreted as being due to a peculiar velocity of the scattering plasma (similar to 20 pc distant), and not due to any changes within the source itself. We discus's the source structure on a size of tens of microarcseconds, and illustrate how such a monitoring campaign can yield such, information.

Abstract:

We do not fully understand the dynamics and evolution of a radio galaxy. Models of classical double (FR II; Fanaroff & Riley 1974) sources are in a reasonable state, but these objects are rare. Non-FRII sources (generically called FRI) axe far more common, but much less well understood. In this paper I use the data to suggest possible new models for FRI sources, and discuss, the physical questions which these new models raise.