Measuring gravitational-wave higher-order modes

We investigate the observability of higher harmonics in gravitational wave signals emitted during the coalescence of binary black holes. We decompose each mode into an overall amplitude, dependent upon the masses and spins of the system, and an orientation-dependent term, dependent upon the inclination and polarization of the source. Using this decomposition, we investigate the significance of higher modes over the parameter space and show that the $\ell = 3$, $m = 3$ mode is most significant across much of the sensitive band of ground-based interferometric detectors, with the $\ell = 4$, $m = 4$ having a significant contribution at high masses. We introduce the higher mode signal-to-noise ratio (SNR), and show that a simple threshold on this SNR can be used as a criterion for observation of higher harmonics. Finally, we investigate observability in a population of binaries and observe that higher harmonics will only be observable in a few percent of binaries, typically those with unequal masses and viewed close to edge-on

Evidence for subdominant multipole moments and precession in merging black-hole-binaries from GWTC-2.1

The LIGO--Virgo--KAGRA collaborations (LVK) recently produced a catalogue containing gravitational-wave (GW) observations from the first half of the third GW observing run (O3a). This catalogue, GWTC-2.1, includes for the first time a number of \emph{exceptional} GW candidates produced from merging black-hole-binaries with unequivocally unequal component masses. Since subdominant multipole moments and spin-induced orbital precession are more likely to leave measurable imprints on the emitted GW from unequal component mass binaries, these general relativistic phenomena may now be measurable. Indeed, both GW190412 and GW190814 have already shown conclusive evidence for subdominant multipole moments. This provides valuable insights into the dynamics of the binary. We calculate the evidence for subdominant multipole moments and spin-induced orbital precession for all merging black-hole-binaries in GWTC-2.1 that were observed during O3a and show that (a) no gravitational-wave candidate has measurable higher order multipole content beyond $\ell = 3$, (b) in addition to the already known GW190412 and GW190814, GW190519\_153544 shows significant evidence for the $(\ell, |m|) = (3, 3)$ subdominant multipole, (c) GW190521 may have measurable subdominant multipole content and (d) GW190412 may show evidence for spin-induced orbital precession.Comment: 18 pages, 6 figure

Compact binary astrophysics

This thesis brings together several projects in compact binary astrophysics that intersect at two main loci. The first being calculations of the science that is possible with future gravitational-wave detectors. On this front, chapter 2 provides localization estimates for a variety of future gravitational-wave network configurations, to inform the science case and observing strategies for future gravitational and electromagnetic detectors. In chapter 3 we predict the constraints that future observations will make on the inclination of the orbital plane of compact binaries. Finally, chapter 7 explores the observability and parameter estimation of seed black holes with future gravitational-wave networks. The second focus of this thesis is determining what is measurable in a gravitational-wave signal emitted in a binary coalescence. In chapter 3, we describe in detail degeneracies in the amplitude of the dominant emission of the two gravitational-wave polarizations, which limits our ability to measure their luminosity distance. Chapter 4 describes how higher harmonics in the waveform can break these degeneracies and introduces a simple criterion for their observation. Using this criterion, and a related one for precession, in chapters 5 and 6 we explore the evidence for higher harmonics and precessions in the signals detected in the first half of LIGO-Virgo's third observing run

Do paramedics have a professional obligation to work during a pandemic? A qualitative exploration of community member expectations

Objectives: Previous research has identified a lack of clarification regarding paramedic professional obligation to work. Understanding community expectations of paramedics will provide some clarity around this issue. The objective of this research was to explore the expectations of a sample of Australian community members regarding the professional obligation of paramedics to respond during pandemics. Methods: The authors used qualitative methods to gather Australian community member perspectives immediately before the onset of the coronavirus disease 2019 (COVID-19) pandemic. Focus groups were used for data collection, and a thematic analysis was conducted. Results: The findings revealed 9 key themes: context of obligation (normal operations versus crisis situation), hierarchy of obligation (individual versus organizational obligation), risk acceptability, acceptable occupational risk (it’s part of the job), access to personal protective equipment, legal and ethical guidelines, education and training, safety, and acceptable limitations to obligation. The factors identified as being acceptable limitations to professional obligation are presented as further sub-themes: physical health, mental health, and competing personal obligations. Conclusions: The issue of professional obligation must be addressed by ambulance services as a matter of urgency, especially in light of the COVID-19 coronavirus pandemic. Further research is recommended to understand how community member expectations evolve during and after the COVID-19 coronavirus pandemic

Deeper, Wider, Sharper: Next-Generation Ground-Based Gravitational-Wave Observations of Binary Black Holes

Next-generation observations will revolutionize our understanding of binary black holes and will detect new sources, such as intermediate-mass black holes. Primary science goals include: Discover binary black holes throughout the observable Universe; Reveal the fundamental properties of black holes; Uncover the seeds of supermassive black holes.Comment: 14 pages, 3 figures, White Paper Submitted to Astro2020 (2020 Astronomy and Astrophysics Decadal Survey) by GWIC 3G Science Case Team (GWIC: Gravitational Wave International Committee

Identifying heavy stellar black holes at cosmological distances with next generation gravitational-wave observatories

We investigate the detectability of single-event coalescing black hole binaries with total mass of $100-600 M_{\odot}$ at cosmological distances ($5 \lesssim z \lesssim 20$) with the next generation of terrestrial gravitational wave observatories, specifically Einstein Telescope and Cosmic Explorer. Our ability to observe these binaries is limited by the low-frequency performance of the detectors. Higher-order Multipoles of the gravitational wave signal are observable in these systems, and detection of such multipoles serves to both b the mass range over which black hole binaries are observable and improve the recovery of their individual masses and redshift. For high redshift systems of $\sim 200 M_{\odot}$ we will be able to confidently infer that the redshift is at least $z=12$, and for systems of $\sim 400 M_{\odot}$ we can infer a minimum redshift of at least $z=8$. We discuss the impact that these observations will have in narrowing uncertainties on the existence of the pair-instability mass-gap, and their implications on the formation of the first stellar black holes that could be seeds for the growth of supermassive black holes powering high-$z$ quasars.Comment: 19 pages, 16 figure

Of babies and bath water: Is there any place for Austin and Grice in interpersonal pragmatics?

This paper discusses a particular strand of interpersonal pragmatics that may be known as ‘discursive’ pragmatics and attempts to delineate what is entailed in such an approach. Some scholars may characterise it as placing emphasis on participant evaluations, others may foreground the analysis of contextualised and sequential texts, while still others consider it to include both of these. In general, though, discursive pragmatics often seems to involve a reaction to, and a contrast with, so-called Gricean intention-based approaches. In this paper I argue that, far from discarding the insights of Grice, Austin and others, a discursive approach to interpersonal pragmatics should embrace those aspects of non-discursive pragmatics that provide us with a ‘tool-kit’ and a vocabulary for examining talk-in-interaction. At the same time, I will argue that the shortcomings of the speaker-based, intention- focused pragmatics can be compensated for, not by privileging hearer evaluations of meaning, but by taking an ethnographic and, to some extent, ethnomethodological approach to the analysis of naturally-occurring discourse data. By providing a critique of Locher and Watts’ (2005) paradigmatic example of a discursive approach to politeness and then a sample analysis of interactional data, I demonstrate how a combination of insights from Gricean pragmatics and from ethnomethodology allows the analyst to comment on the construction and negotiation of meaning in discourse, without having recourse to notions of either intention or evaluation

Identifying coherent patterns of environmental change between multiple, multivariate records: an application to four 1000-year diatom records from Victoria, Australia

Empirical orthogonal functions (EOFs) of indirect archives of environmental change are increasingly used to identify coherent trends between palaeoclimate records, to separate externally forced patterns from locally driven idiosyncrasies. Lake sediments are particularly suited to such syntheses: they are abundant in most landscapes and record a wide array of information, yet local complexities often conceal or confuse the climate signal recorded at individual sites. Lake sediment parameters usually exhibit non-linear, multivariate and indirect responses to climate, therefore identifying coherent patterns between two or more lake records presents a complex challenge. Ideally, the selection of representative variables should be non-subjective and inclusive of as many different variables as possible, allowing for unexpected correlations between sites. In order to meet such demands, we propose a two-tier ordination procedure whereby site-specific (local) ordinations, obtained using Detrended Correspondence Analysis (DCA), are nested within a second, regional EOF. Using the local DCAs as representative variables allows the retention of a larger fraction of variance from each site, removes any subjectivity from variable selection and retains the potential for observing multiple, coherent signals from within and between each dataset. We explore this potential using four decadally resolved diatom records from volcanic lakes in Western Victoria, Australia. The records span the 1000 years prior to European settlement in CE 1803. Our analyses reveal at least two coherent patterns of ecological change that are manifest in each of the four datasets, patterns which may have been overlooked by a single-variable, empirical orthogonal function approach. This intra-site coherency provides a valuable step towards understanding multi-decadal hydroclimate variability in southeastern Australia