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Mathematisch-Naturwissenschaftliche Fakultät - Jahrgang 2013

 

Titel Multi-wavelength studies of pulsars and their companions
Autor Ioannis (John) Antoniadis
Publikationsform Dissertation
Abstract Neutron stars are the degenerate relic cores of massive stars formed in the aftermath of a supernova explosion. Matter in their centes is believed to be condensed at densities as high as ten times that found in atomic nuclei. Thus, observational access to their properties provides the means to study the behavior of physical laws in extreme conditions, beyond the reach of terrestrial experiments. Rapidly rotating, highly magnetized neutron stars emit a narrow intense beam of radio emission from their magnetospheric poles. When this pulse happens to intersect our line of sight, it gives rise to the pulsar phenomenon. Regular radio-timing of pulse arrival times on earth, results in some of the most precise measurements in astrophysics. This thesis deals with the study of binary millisecond pulsars with white dwarf companions and is divided in 7 Chapters.
Chapters 1 & 2 give a brief introduction to neutron stars, pulsars, and binary pulsars.
Chapter 3 describes spectroscopic and optical observations of the low mass white dwarf companion to PSR J1909-3744. For this system, radio observations have yielded a precise mass measurement as well as distance information. Combined with the optical data, these provide the first observational test for theoretical white-dwarf cooling models and spectra. The latter, if reliable, can be used to infer theory-independent masses for similar systems.
In Chapter 4, I discuss the measurement of the component masses in the short-orbit PSR J1738+0333 system based on spectroscopy of its white-dwarf companion. This system is particularly important for understanding the physics of pulsar recycling and binary evolution. Moreover, combined with the measurement of the orbital decay from radio-timing, the masses pose the most stringent constraints on Scalar-Tensor gravity.
Chapter 5 describes radio and optical observations of PSR J0348+0432, a compact pulsar-white dwarf binary discovered recently with the 100-m Green-Bank Radio Telescope. Spectral observations of its bright white-dwarf companion show that the neutron star in the system is the most massive known to date. This measurement is based on a new set of white-dwarf cooling models, designed to take into account the remaining uncertainties not constrained by PSR J1909-3744. Furthermore, I discuss radio-timing observations that have yielded a significant measurement of the orbital decay which is completely consistent with the General Relativity prediction. This provides a verification of the theory in a highly non-linear gravitational regime, far beyond the reach of previous experiments. PSR J0348+0432 also poses significant constraints on the equation-of-state at supra-nuclear densities and sheds light to the evolution of low-mass X-ray binaries.
In Chapter 6, I present the detection of the optical counterpart of the 1 solar mass companion to PSR J1141-6545 that verifies its white-dwarf nature. This simple observation is particularly important for understanding the unique evolutionary history of the binary and justifies the constraints on alternative-gravity theories imposed by the system.
Finally, Chapter 7 summarizes the main conclusions of this work.
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© Universitäts- und Landesbibliothek Bonn | Veröffentlicht: 25.09.2013