Jaron, Frédéric Felix Daniel: Physical processes behind the periodic radio and gamma-ray emission from the X-ray binary LS I +61°303. - Bonn, 2016. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-44211
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-44211,
author = {{Frédéric Felix Daniel Jaron}},
title = {Physical processes behind the periodic radio and gamma-ray emission from the X-ray binary LS I +61°303},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2016,
month = jul,

note = {X-ray binaries are binary stars composed of a normal star and a compact object which, via Roche-lobe overflow or wind accretion, accretes matter from the companion. X-ray emission from these objects can be either thermal emission from an accretion disk formed around the compact object, or the result of inverse Compton scattering. Emission in the radio regime is synchrotron emission from relativistic electrons gyrating in the magnetic fields of a jet. Some X-ray binaries are also emitters of -ray emission, the physical processes behind the nonthermal emission of these objects are still poorly understood. Subject of this thesis is the investigation on physical processes behind the emission from one particular -ray-loud X-ray binary, LS I +61°303. This source is composed of a Be type star and a compact object of still unknown nature, i.e., either a neutron star or a black hole. Accretion onto the compact object along the eccentric orbit of this source is predicted to peak twice per orbit, giving rise to emission all over the electromagnetic spectrum modulated by the orbital period P1 ≈ 26:5 days. Analysis of the astrometry of VLBI images of the source resulted in a precession period of a jet of 27–28 days, expected to give rise to periodic variable Doppler boosting. Timing analysis of archived radio data revealed that a compatible period of P2 ≈ 26:9 days modulates the radio lightcurve in addition to P1, giving rise to a beating with a long-term period of ∼ 4:5 years, in agreement with previous findings. The methods employed for this thesis are timing analysis of radio and GeV lightcurves, and the modelling of physical processes which can lead to radio and GeV emission from LS I +61°303. The first result of this thesis is how the knowledge about the beating between the periodic ejection of particles and the jet precession can be used for a straightforward prediction of the radio outbursts observable by radio telescopes. The GeV light curve has previously been reported to peak around periastron only. The second result presented here is the discovery of a periodic apastron GeV peak, also explaining a previously reported disappearance of the orbital period from the power spectrum of the GeV light curve during some epochs. We further find that, while the apastron GeV peak is modulated by P1 and P2, the periastron GeV peak is only modulated by P1. This timing characteristic is explained by a physical model of a self-absorbed, adiabatically expanding jet, refilled with a population of relativistic electrons twice along the orbit, the bulk velocity of the jet being slower at periastron than at apastron, giving rise to smaller variable Doppler boosting at periastron, and consequently, P2 is not present in the power spectrum during these orbital phases. In addition, the absence of a periastron radio peak is explained by catastrophic inverse Compton losses of the electrons at periastron, leading to a jet too short for radio emission. We further report on the detection of radio emission of the first proven case of a binary star composed of a Be type star and a black hole, MWC 656, a source which has also been detected in the GeV regime and therefore bears resemblance to LS I +61°303. The source LS I +61°303 does not only feature variability in the order of months to years, but there is also evidence for short-term variability over time scales of days and shorter. We observed LS I +61°303 with the 100-m telescope in Effelsberg, quasi-simultanously at three radio frequencies with unprecedented sampling rate for a multiwavelength observation of this source. We present our results on possible periodic behavior on time-scales of hours, which can possibily contribute to future investigations on transient phenomena related to the jet. In conlcusion, we show that an accretion scenario for LS I +61°303, including a precessing relativistic jet, can explain the periodic emission from this X-ray binary and may help to understand the physical processes in related sources.},
url = {https://hdl.handle.net/20.500.11811/6846}

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