Pulsars, transients and relativistic astrophysics

Abstract:

We briefly review the inverse-Compton (IC) scattering of nuclear photons in the lobes of radio galaxies and quasars. We concentrate on the possibility of testing this model with the Chandra observatory and of constraining the electron energy distribution by measuring the Xray fluxes produced by this effect. We also discuss the evidence for IC scattering of nuclear photons in powerful radio galaxies.

Abstract:

A new model for the so called cluster radio relics is presented (see Ensslin & Gopal-Krishna 2001 for more details). Fossil radio cocoons, resulting from the former activity of radio galaxies, should contain a low energy relativistic electron population and magnetic fields. Even electrons with ages as high as 2 Gyr can be re-accelerated adiabatically to radio- emitting energies, if the fossil radio plasma gets compressed in an environmental shock wave. Such a wave can be caused by merging events in galaxy clusters, or by accretion onto clusters. An implication of this model is the existence of a population of diffuse, ultra-steep spectrum, very low-frequency radio sources located inside and possibly outside of clusters of galaxies, tracing the revival of aged fossil radio plasma by the shock waves associated with large-scale structure formation.

Abstract:

Multi-frequency radio observations of a powerful classical double radio galaxies can be used to determine the beam power of the jets emanating from the AGN, the total time the source will actively produce jets, and the total energy available to power the jets during their lifetime. Empirical determinations of these quantities are presented for 20 classical double radio galaxies. The model assumptions, trends with redshift, and implications for energy extracted from central engines are discussed.

Abstract:

Results from Chandra observations of the two nearest, powerful radio galaxies are summarised.

Abstract:

We discuss the detection of variable circular. polarization (CP) in several scintillating radio sources: PKS 1519-273, PKS 0405-385 and Sgr A*. The CP in PKS 1519-273 is strong, and varies on a timescale of hours to days at frequencies between 1.4 and 8.6 GHz. We argue that the variability is due to scintillation of a compact (15 - 35 muas) component of the source with -3.8 +/- 0.4% circular polarization at 4.8 GHz. We find that no simple model can account for the magnitude and spectrum of the circular polarization in this source. We also interpret the variable CP observed in PKS 0405-385 in terms of scintillation, although the behaviour of the CP is more complicated, and changes character between scintillation epochs. We also discuss CP in Sgr A*, which is found to be variable at 2.5 and 1.4 GHz on a timescale similar to 7 days. The fractional degree of variability in circular polarization greatly exceeds that in total intensity in all three sources.