A theoretical study of relativistic jets and accretion processes

Abstract

The following work explores different aspects of the disc:jet connection in X-ray binaries. There is a detailed description of a new jet model (iShocks) that is used, firstly, to address the re-energization problem in the conical jet geometries. The adiabatic energy losses suffered by conical jets are successfully countered to reproduce the canonical flat/inverted synchrotron spectrum associated with compact radio jets.

The iShocks model uses discrete packets of plasma, or shells, to simulate a jet. The shell collisions give rise to the shocks that are used to re-energize the emitting electrons. Multiple internal shocks, all along the jet, are shown to be necessary to achieve sufficient re-acceleration. The flat/inverted spectrum (ranging from the infra-red to the radio) is successfully reproduced and the high frequency break for such a spectrum is shown to be correlated with the jet power: v_b ~ L^0.6_W. While the flat-spectrum synchrotron flux is also correlated with the jet power via: F_v ~ L^1.4_W. Both these correlations are in agreement with the previous analytical predictions. The model is also used to explore themassive ejections scenario in the source GRS 1915+105. Various iShocks set-ups are used to model the data that display the flaring behaviour observed in different frequencies (IR-mm-radio).

The X-ray binary timing properties are also investigated with the aide of the iShocks model. In particular, the optical/X-ray correlations are the focus of the present study. These correlations have been observed to show some interesting behaviours, such as: the optical lagging the X-rays, and the optical emission showing awareness of the X-ray emission in the form of pre-cognition dips. A number of these correlations are successfully reproduced by translating the simulated X-ray light curves into the jet parameters used as the input for the iShocks model.

In addition to relativistic jets, a study of the electron-positron pair processes is also included in the present work. The electron-positron pair annihilation is implemented in an existing Comptonization code (simulating the corona) to explore the possibility of masking an annihilation line from the X-ray binary sources. The results show that radiative processes such as inverse Compton scattering and bremsstrahlung radiation, in addition to thermal line broadening, can be very effective in making the e^-/e⁺ annihilation line indistinguishable from the rest of the high energy spectrum.

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