Final Report Summary - COMPACT BINARIES (Compact Binaries as Gravitational-Wave Sources)
Compact binaries, consisting of two compact objects (white dwarfs, neutron stars, and black holes) orbiting each other, are strong sources of Gravitational waves (GWs). During past years, significant progress was made in GW experiments. The US-based LIGO detector reached its designed sensitivity in 2005. Upgrades of the LIGO and the European Virgo detectors started at the end of 2010. The Advanced LIGO and Virgo detectors, which will be about ten times more sensitive than their predecessors, will start observations in 2015. With the encouraging prospects for detecting GWs from compact binaries, astrophysical understanding of these objects is crucial in order to assess the performance of the currently operating GW detectors as well as to predict prospects for the future generation detectors.
The main objective of this project was to explore the implications of compact binaries in the context of the GW detection. During her time as a Marie-Curie fellow at Lund Observatory, the Researcher (Chunglee Kim) carried out the following projects summarised below.
A. Galactic pulsar population: The researcher published a paper on 'Pulsar Binary Birthrates with Spin-Opening Angle Correlations'' with her collaborator Richard O'Shaughnessy (Penn State University, United States (US); currently affiliated to the University of Wisconsin-Milwaukee). Pulsars are strongly magnetised fast spinning neutron stars. The main advantage of using known pulsar binaries is that one can calculate galactic birthrates of neutron star binaries based on observations, which are considered to be more reliable than theoretical estimates. Considering five pulsar-neutron star and four pulsar-white dwarf binaries known in the galactic disk, the Researcher and her collaborator calculated probability density functions of the pulsar beaming fractions and updated the galactic birthrates of pulsar binaries based on the best observational constraints. Currently, no black hole binaries are known. This work can applied to pulsar-black hole binaries, when observations are available in the future.
B. GRB phenomenology: Gamma-ray bursts (GRBs), strongly collimated gamma-ray emission that lasts only seconds to minutes, are another important GW source that can be detectable on the ground. A canonical GRB model involves an accretion disc around a compact object (e.g. black hole). Recent observations made by the US Swift satellite revealed that more than 30 % of GRBs show flares in X-rays about 100-1000 seconds after the prompt gamma-ray emission The researcher modelled a GRB model that can explain the observed X-ray flares in collaboration with Melvyn B. Davies (Lund, the project's coordinator), Ross Church (Lund), and Andrew Levan (Warwick). If a supernova explosion occurred in a tight orbit, some of the mass ejected from a new-born compact object may remain bound to the system. Depending on model assumptions, the researcher and her collaborators found that it is possible to form a fall back disc around the compact object(s) in the binary, which can power the X-ray flares on the timescales that are consistent with observations.
C. Compact binaries and GW detection: The researcher's work on galactic pulsar binaries was included in the recent paper by the LIGO scientific collaboration (LSC) and Virgo collaboration, 'Predictions for the rates of compact binary coalescences observable by ground-based gravitational-wave detectors'. This paper presents a up-to-date, comprehensive summary of the detection rates predicted by both empirical and theoretical models for all types of compact binaries that can be detectable by ground-based GW detectors (e.g. pulsar binaries and black hole binaries).
The main objective of this project was to explore the implications of compact binaries in the context of the GW detection. During her time as a Marie-Curie fellow at Lund Observatory, the Researcher (Chunglee Kim) carried out the following projects summarised below.
A. Galactic pulsar population: The researcher published a paper on 'Pulsar Binary Birthrates with Spin-Opening Angle Correlations'' with her collaborator Richard O'Shaughnessy (Penn State University, United States (US); currently affiliated to the University of Wisconsin-Milwaukee). Pulsars are strongly magnetised fast spinning neutron stars. The main advantage of using known pulsar binaries is that one can calculate galactic birthrates of neutron star binaries based on observations, which are considered to be more reliable than theoretical estimates. Considering five pulsar-neutron star and four pulsar-white dwarf binaries known in the galactic disk, the Researcher and her collaborator calculated probability density functions of the pulsar beaming fractions and updated the galactic birthrates of pulsar binaries based on the best observational constraints. Currently, no black hole binaries are known. This work can applied to pulsar-black hole binaries, when observations are available in the future.
B. GRB phenomenology: Gamma-ray bursts (GRBs), strongly collimated gamma-ray emission that lasts only seconds to minutes, are another important GW source that can be detectable on the ground. A canonical GRB model involves an accretion disc around a compact object (e.g. black hole). Recent observations made by the US Swift satellite revealed that more than 30 % of GRBs show flares in X-rays about 100-1000 seconds after the prompt gamma-ray emission The researcher modelled a GRB model that can explain the observed X-ray flares in collaboration with Melvyn B. Davies (Lund, the project's coordinator), Ross Church (Lund), and Andrew Levan (Warwick). If a supernova explosion occurred in a tight orbit, some of the mass ejected from a new-born compact object may remain bound to the system. Depending on model assumptions, the researcher and her collaborators found that it is possible to form a fall back disc around the compact object(s) in the binary, which can power the X-ray flares on the timescales that are consistent with observations.
C. Compact binaries and GW detection: The researcher's work on galactic pulsar binaries was included in the recent paper by the LIGO scientific collaboration (LSC) and Virgo collaboration, 'Predictions for the rates of compact binary coalescences observable by ground-based gravitational-wave detectors'. This paper presents a up-to-date, comprehensive summary of the detection rates predicted by both empirical and theoretical models for all types of compact binaries that can be detectable by ground-based GW detectors (e.g. pulsar binaries and black hole binaries).