Sharma, Richa: Properties of relativistic jets in X-ray binaries. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc:
author = {{Richa Sharma}},
title = {Properties of relativistic jets in X-ray binaries},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = jul,

note = {X-ray binaries are stellar systems consisting of a compact object (either a neutron star or a black hole) accreting matter from a companion star. Some of the X-ray binaries form relativistic jets where plasma accelerates close to the speed of light. Relativistic jets have been extensively studied, and the most advanced research in this field investigates their structure, jet’s core position and short-term flaring events.
In this thesis, we initially work on understanding the structure of the jet wherein jet particles flow continuously. Radio observations have shown that the jet core for different frequencies is located at different positions along the jet axis, known as the core-shift effect. Additionally, jets show a flat spectrum in their emission over a range of frequencies. In the first project, we use a semi-analytical code of a synchrotron emitting, self-absorbed jet to find the relationship between the core-shift and flat spectrum. We study the jet characteristics by varying different parameters in the jet model. Our main results from this analysis are that the core moves upstream when the jet is viewed at a larger inclination angle and makes the spectra steeper. Our analytical results corroborate and explain the observed anisotropy of spectral index with the inclination angle. Additionally, when the relativistic electron density increases in the jet, the core moves downstream, making the spectra flatter. Thus, both core position and spectra are related and vary due to opacity change along the line of sight.
After investigating the jet properties where particles are continuously flowing, we study the jet’s case with transient particle injection episodes. In a few X-ray binaries, short-term variability is superimposed on the radio and X-ray emission. Therefore, we examine the radio and X-ray properties of an X-ray binary system: LS I +61°303. It is one of the most powerful radio-emitting system, which is highly periodic at all wavelengths over a time-scale of one month. We use radio data of the source obtained with the Westerbork synthesis radio telescope and X-ray data obtained with the Suzaku telescope. Timing analysis reveals periodic oscillations in the system of ~55 min (radio) stable over four days and ~2.5 h (X-ray) stable for 21 h, albeit at different epochs. We also compare our analysis with data from the literature and find that the periodic oscillations are always related to large radio outbursts but are independent of the outburst’s amplitude. These periodic features, which range from minute to hour time-scales, can be understood as magnetic reconnection events.
Inspecting deeper into the case where particle density in the jet increases abruptly for a short period, we present new simultaneous observations of LS I +61°303 using the XMM–Newton and AMI-LA telescopes. The AMI-LA telescope observed the target source for ~11 h, and XMM–Newton telescope observed it for ~6 h; thus, we obtain simultaneous radio/X-ray data for ~5 h. Using correlation analysis, we establish that the radio and X-ray emission in LS I +61◦303 is correlated up to 81 per cent with zero time-lag. Moreover, after removing the long-term trend from the data, we find that even radio and X-ray emission variability is correlated up to 40 per cent. The results reveal that the radio and X-ray emission is due to the same population of electrons. If future observations can find a significant time-lag between emission at both wavelengths, it could imply either a synchrotron or inverse-Compton emission mechanism for the X-ray wavelengths.
In conclusion, we unify the core-shift and spectral properties in a steady jet. Furthermore, we show that the detection of periodic oscillations and correlation studies between radio and X-ray emission helps us understand X-ray binaries’ physical processes.},

url = {}

The following license files are associated with this item: