Pulsars, transients and relativistic astrophysics

Abstract:

We have accumulated multiwavelength lightcurves for eight black hole X-ray binaries which have been observed to enter a supposed ``soft X-ray transient'' outburst, but which in fact remained in the low/hard state throughout the outburst. Comparison of the lightcurve morphologies, spectral behaviour, properties of the QPOs and the radio jet provides the first study of such objects as a subclass of X-ray transients (XRTs). However, rather than assuming that these hard state XRTs are different from ``canonical'' soft XRTs, we prefer to consider the possibility that a new analysis of both soft and hard state XRTs in a spectral context will provide a model capable of explaining the outburst mechanisms for the majority of black hole X-ray binaries.

Abstract:

We have performed the first full 3-D GRMHD simulation of a Schwarzschild black hole with a freely falling corona. The preliminary simulation results show that the accretion disc is falling with the corona and that the proper pressure increases near the black hole, as in the previous axisymmetric simulations. We expect that in this case an instability around the black hole will occur as a result of the steep pressure gradient and the twisted magnetic fields. We plan to investigate how the instability affects jet formation.

Abstract:

We report on an effort to study the connections between dynamics in simulated radio galaxy plasma flows and the properties of non-thermal electron populations carried in those flows. To do this we have introduced a new numerical scheme for electron transport that allows a much more detailed look at this problem than has been possible before. Especially when the dynamics axe fully three dimensional the flows are generally chaotic in the cocoon, and the jet itself can flail about violently. The bending jet can pinch itself off and redirect itself to enhance its penetration of the ambient medium. These behaviours often eliminate the presence of a strong jet termination shock, which is assumed present in all modern cartoon models of the radio galaxy phenomenon. Instead a much more complex "shock web" forms near the end of the jet that leads to a far less predictable pattern of particle acceleration. Similarly, the magnetic fields in these flows are highly filamented, as well as spatially and temporally intermittent. This leads to a very localized and complex pattern of synchrotron aging for relativistic electron populations, which makes it difficult to use properties of the electron spectrum to infer the local rate of aging.

Abstract:

We show results from a 7 year VLBI monitoring programme of 3C 273 at millimetre wavelengths. We find evidence for component acceleration, motion or rotation of fluid dynamical patterns, and an outburst-ejection relation between gamma-ray flares and, new jet components.