The astrophysics of energetic x-ray binaries

This thesis is a study of the X-ray binary Cygnus X-3, and related objects, using primarily observations at radio, sub-rom and infrared wavelengths. I find the emission mechanism to be synchrotron in the radio and sub-mm, while the infrared emission is thermal from the hot wind. The upper limit to the synchrotron emission is interpreted as being due to spectral ageing and implies a magnetic field strength of 7 T at a distance of 700 Rʘ from the centre of the system. The nature of the companion star in Cyg X-3 was investigated by midinfrared observations using the ISO satellite. I find that the spectrum shows a steady decrease and flattening at longer wavelengths which is consist ant with a standard wind emission. Thus the complete quiescent spectrum from Cyg X-3 shows two different emission mechanisms and covers a full 5 decades of frequency. High sensitivity and high time resolution radio photometry, taken during a minor flare period, reveal rapid (10 minute) increases and decreases in intensity which severely constrain the size of plasmons. Brightness temperatures of typically 1010K are found. I also consider models for the superluminal expansion and contraction of the Cyg X-3 source, observed on a milli-arcsecond scale by LIewell et al. (1998). The elliptical shape and the superluminal contraction are particularly hard to explain. Models involving photon beams illuminating shells, or propagating photon patterns are the most plausible. A thorough survey for maser emission from these sources has produced strong upper limits and improved our understanding of the circumstellar environment ofCyg X-3. This thesis has probed the radio-jet X-ray binaries, and made significant advances, opening up more questions about the nature of these sources and new areas of research

THE UN AND THE GLOBAL COMMONS

SUMMARY The UN's record on the global commons is mixed: remarkable success in arresting the damage done to the ozone layer, a promising start in confronting the threat of global warming, but a protracted failure, at its Third Law of the Sea Conference, in the search for a generally acceptable regime to govern sea?bed mining. This failure is now somewhat redeemed by the 1994 agreement which, however, heavily favours the sea?bed miners. Overall, the UN seems better at averting threats to the commons than at sharing the benefits from exploiting them; but it has shown an admirable capacity to learn from its mistakes

Comments on the superluminal motion in Cygnus X-3

Following the recent discovery that Cyg X-3 exhibits superluminal motion, the implications of superluminal expansion and contraction are investigated. We propose that the effect is due to either a propagating photon pattern or to outwardly moving shells illuminated by an intense beam of radiation.Comment: accepted for publication in MNRAS; 5 pages, 3 figure

Development of Activism: The Elders of the Anti-nuclear Movement

The US anti-nuclear movement formed in opposition to the development of nuclear weapons and energy. Anti-nuclear activists have rallied since the late 1970’s opposed to the construction of Plant Vogtle near Waynesboro, Georgia due to the social and environmental justice issues related to the nuclear industry. In 2010, the nuclear industry proposed a nuclear resurgence in the US, proposing to construct new reactors at Plant Vogtle. This represented the first time new nuclear reactors had been proposed since the moratorium on new reactors as a result of the partial meltdown at Three Mile Island in 1979. The aim of the study is to understand the experience of “first wave” anti-nuclear activists in Georgia (those engaged for twenty years or more). Bronfenbrenner’s Ecological Framework was employed to locate anti-nuclear activists’ perceived facilitators and barriers to their activism. Semi-structured interviews with these activists yielded rich descriptions about their experience in the anti-nuclear movement. Activists endorsed facilitators and barriers related to individual characteristics however, the majority of activists perceived facilitators and barriers beyond the individual level. Specifically, the majority of activists mentioned facilitators and barriers relating to the media and political systems and the power and resource imbalances within society. The role of community psychology is discussed in relation to this field of inquiry

Modelling of Infrared emission from Cyg X-3 and the UKIRT IRCAM3 point spread function

Modelling of the point spread function of the UKIRT IRCAM3 array was conducted in order to test any extended emission around the X-ray binary Cyg X-3. We found that the point spread function cannot be represented by a simple Gaussian, but modelling of the stars required additional functions namely Lorrentzian and exponential components. After modelling for the PSF, we found that Cyg X-3 could be represented by two stellar-type profiles, 0.56" apart.Comment: 7 pages, 4 figures, to appear in Vistas in Astronomy as part of a conference at Jodrell Bank, Apr 96, Relative Jets in X-ray binaries. Style files include

Excess sub-millimetre emission from GRS 1915+105

We present the first detections of the black hole X-ray binary GRS 1915+105 at sub-millimetre wavelengths. We clearly detect the source at 350 GHz on two epochs, with significant variability over the 24 hr between epochs. Quasi-simultaneous radio monitoring indicates an approximately flat spectrum from 2 - 350 GHz, although there is marginal evidence for a minimum in the spectrum between 15 - 350 GHz. The flat spectrum and correlated variability imply that the sub-mm emission arises from the same synchrotron source as the radio emission. This source is likely to be a quasi-steady partially self-absorbed jet, in which case these sub-mm observations probe significantly closer to the base of the jet than do radio observations and may be used in future as a valuable diagnostic of the disc:jet connection in this source.Comment: 5 pages, 3 figures, accepted for publication in MNRA

Role of WT1 in Ischaemic Angiogenesis

Ischaemia causes irreversible tissue damage in cardiovascular disease. Since regenerative angiogenesis fails to consistently induce sufficient reperfusion to facilitate repair, targeted manipulation of angiogenesis is clinically desirable. The Wilms’ tumour suppressor (Wt1) is a transcription factor which regulates numerous genes and cellular processes, including many intrinsic to angiogenesis. We hypothesise that WT1 in the endothelium influences the angiogenic function of endothelial cells. WT1 was identified in endothelial and non-endothelial cells comprising vessel outgrowths generated by cultured aortic rings from WT1-GFP reporter mice. Inducible deletion of WT1 from the endothelium (VE-Wt1 KO) significantly delayed angiogenesis in this assay (p<0.05 relative to controls). In vivo, WT1 expression was evident in vascular endothelial and perivascular cells of the hindlimb as early as 3 days following femoral artery ligation to induce ischaemia, often in cells expressing epithelial and mesenchymal markers simultaneously. However, VE-Wt1 KO had no effect on hindlimb reperfusion (laser Doppler; days 0-28) or on vessel density (day 28). Similarly, VE-Wt1 KO had no effect on vessel density or expression of angiogenic factors (qRT-PCR) in sponges inserted subcutaneously in mice (20 days). To further understand the role of WT1 in angiogenesis, transcriptomic RNA expression analysis was performed in WT1+ and WT1- cells isolated (FACs) from sponges after implantation in WT1-GFP mice. WT1+ cells exhibited higher expression of genes involved in a number of processes relevant to tissue repair, including angiogenesis (p=3.11x10-8), wound healing (p=3.45x10-7) and epithelial-to-mesenchymal transition (EMT) (p=5.86x10-4). These results shed new light on the role of WT1 in ischaemic angiogenesis. In concurrence with previously published work, we show that deletion of endothelial WT1 can delay angiogenesis however, WT1 is not just instrumental in endothelial cells in this context. WT1 has a broader role in tissue repair in ischaemia, in part through regulation of cell transition (EMT). This work has improved our understanding of the regulatory role of WT1 in angiogenesis and repair, while revealing a number of novel insights into the function of WT1. This highlights WT1 as a potentially beneficial therapeutic target to facilitate regeneration in cardiovascular disease