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Precision ephemerides of neutron-star binaries to assist gravitational-wave searches: Sco X-1 & Cyg X-2

Premachandra, Sammanani Shakya ; Duncan K. Galloway

2014

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  • Título:
    Precision ephemerides of neutron-star binaries to assist gravitational-wave searches: Sco X-1 & Cyg X-2
  • Autor: Premachandra, Sammanani Shakya ; Duncan K. Galloway
  • Assuntos: Accretion ; Accretion discs - binaries ; Binaries - X-rays ; Ephemerides ; Gravitational waves ; Individual (Cyg X-2) ; Individual (GR Mus) ; Individual (GX 9+9) ; Individual (Sco X-1) ; Individual (V801 Ara) ; Individual (V926 Sco) ; Neutron - techniques
  • Descrição: Accreting neutron stars in low-mass X-ray binaries (LMXBs) are candidate persistent high-frequency gravitational wave (GW) sources, which may be detectable with next generation interferometers such as Advanced LIGO/VIRGO within this decade. However, the search sensitivity is likely limited principally by the uncertainty in the binary orbital parameters. In the first part of the thesis I performed optical spectroscopy of two low-mass X-ray binaries, Sco X-1 and Cyg X-2 observed at the William Herchel Telescope (WHT) in La Palma, the Very Large Telescope (VLT) in Chile, and the Liverpool Telescope (LT) in La Palma. Circular orbit fits to the the radial velocity measurements from the two optical counterparts combined with the historical radial velocity measurements, provide an improved set of orbital parameters. For the case of Sco X-1, I obtained an improvement of a factor of 2 in the orbital period (Porb) precision and factor of 2.5 in the phase error T0. The newly derived orbital period is consistent with the previous value of Gottlieb et al. (1975). However, the new T0 and the velocity amplitude of the Bowen lines demonstrate a significant shift, which I attribute to changes in the emission geometry between the two epochs. For Cyg X-2, I obtained an improvement of a factor of 2.6 in the orbital period precision and a factor of 2 in the epoch of inferior conjunction, T0. The newly derived orbital parameters for Cyg X-2 imply a mass function of 0.65 +/- 0.01 M☉, leading to a primary mass (M1) of 1.67 +/- 0.22 M☉ (for i = 62.5 +/- 4°). In addition, I estimated the likely orbital parameter precision through to the expected “Advanced" detector observing epochs (2015-) and quantified the improvement in sensitivity via the required number of search templates. The current fractional reduction in the number of templates for the parameters of Sco X-1 and Cyg X-2 is a factor of 5. The last chapter of the thesis investigates the morphology of other low-mass X-ray binaries using Doppler tomography and compare that with the maps of Sco X-1 and Cyg X-2. Finally, I present a catalogue of Doppler maps of various types of binaries published in refereed journals in the last 25 years. Source: TROVE
  • Data de criação/publicação: 2014
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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