System design for the square kilometre array : new views of the universe

The Square Kilometre Array (SKA) radio telescope is being designed as a premier scientific instrument of the 21st century, using novel technologies to maximise its scientific capability. The SKA has an aggressive project timeline, dynamic and evolving scientific requirements, and a large design exploration space with many interdependent sub-systems. These complexities increase the difficulty in developing cost-effective design solutions that maximise the scientific capability of the telescope within construction and operations funding constraints.To gain insight into specific design challenges in this thesis, I have developed parametric models of the telescope system that relate cost to key performance metrics. I examine, as case studies, three aspects of the SKA design that have had little investigation compared to the rest of the telescope to date, but show considerable potential for discovering new astronomical phenomena.First, I present fast transient survey strategies for exploring high time resolution parameter space, and consider the system design implications of these strategies. To maximise the scientific return from limited processing capacity, I develop a new metric, ‘event rate per beam’, to measure the cost-effectiveness of the various search strategies. The most appropriate search strategy depends on the observed sky direction and the source population; for SKA Phase 1, low-frequency aperture arrays tend to be more effective for extragalactic searches, and dishes more effective for directions of increased scatter broadening, such as near the Galactic plane.Second, I compare the cost of two design solutions for low-frequency sparse aperture array observations (70–450 MHz) that achieve similar performance: a single-band implementation with a wideband antenna design; and a dual-band implementation, with each array observing approximately half the fractional bandwidth. Perhaps somewhat surprisingly, despite the dual-band array having twice the number of antenna elements, neither a representative single or dual-band implementation is cheaper a priori, although the uncertainties are currently high. In terms of the broader telescope system design, I show that the central processing, antenna deployment and site preparation costs are potentially significant cost drivers that have so far had insufficient attention.Third, the recent site decision gives rise to the question of how to cost-effectively provide data connectivity to widely separated antennas, to enable high angular resolution observations with the SKA dish array in Africa. To facilitate the design of such a data network, I parametrise the performance and cost of an exemplar network using three simple metrics: maximum baseline length; number of remote stations (grouped antennas) on long baselines; and the product of bandwidth and number of station beams. While all three metrics are cost drivers, limiting the beam–bandwidth product reduces cost without significantly impacting scientific performance.The complexities of the SKA design environment prevent straightforward analyses of cost-effective design solutions. However, the case studies in this thesis demonstrate the importance of parametric performance and cost modelling of the telescope system in determining cost-effective design solutions that are capable of revealing large regions of unexplored parameter space in the radio Universe. The analytical approach to requirements analysis and performance-cost modelling, combined with pragmatic choices to narrow the exploration space, yields new insights into cost-effective SKA designs. Continuation of this approach will be essential to successfully integrate the forthcoming results from various verifications systems into the SKA design over the next few years

Interferometric Methods

Future radio telescopes promise great advances in resolution and sensitivity. These include the Square Kilometer Array, a two array instrument, in South Africa and Australia. Similarly, the next generation Very Large Array (ngVLA) is being designed for construction in North America. These arrays all promise exceptional advances in sensitivity, angular resolution, and survey speed. The SKA and ngVLA are both specified to have sensitivities at the level of $\mu$Jy's. The SKA-Low instrument will consist of a huge number of dipoles antennas in Australia which is pushing the bounds of current FX correlator technology with $\mathbb{O}(n^2)$ scaling, where $n$ is the number of antennas. The design proposals for these instruments include a dense core of antennas, necessitating advances in imaging methods for these very dense cores versus more traditionally sparse instruments. Another ambitious experiment is the Hydrogen Epoch of Reionisation Array (HERA) in South Africa which hopes to make the first direct detection of the Epoch of Reionisation through the red-shifted H{\sc i} signal which is a factor of $10^{5}$ smaller than the thermal-like noise. In this thesis, these problems are tackled by re-examining the underlying principles of interferometry. The first working example of a direct imaging correlator is presented which allows images to be formed directly from the voltages off each antenna in a dense array, without an expensive cross-correlation operation as is typically required. A detailed discussion is given of how standard steps in interferometric imaging differ in this new scheme, including calibration. Additionally the first wide field direct imaging correlator is presented, which allows the problems of non-coplanarity to be dealt with for both sparse and dense arrays in a very efficient manner on modern GPU compute hardware. These are, to the best of the authors knowledge, the only working implementations of a direct imaging correlator for generic arrays with no restrictions on the geometry of the array or homogeneity of constituent receiver elements. These new approaches have been published in the scientific literature as discussed in the Declaration. Moving on from this, the closure phase bispectrum is presented as a way of uncovering the cosmological Epoch of Reionisation signal from the H{\sc i} line. This is using the HERA telescope, which consists of a dense core of parabolic antennas in a highly redundant layout. A data reduction and processing pipeline for the HERA telescope is constructed and presented, for use with the bispectrum. Initial results towards a cosmologial limit are reported. The HERA telescope relies on redundancy in its antenna elements for its calibration and measurement strategy. The bispectrum with its unique mathematical propeties, in combination with forward modelling, is shown to be a potent tool for probing departures from the assumed reudundancy. It is shown, through this method, that HERA suffers significant direction-dependent non-redundancies in the dataset used for our analysis, which are extremely difficult to calibrate out. Finally, the problem of wide-field imaging in next generation arrays is tackled through the development and implementation of a new scheme of wide field imaging. This uses a new method of parallelising the problem of wide-field imaging, and is intended for use with the very large datasets that will be produced by upcoming instruments. Two schemes are introduced: $w$-towers, and Improved $w$-towers. The latter generalises the former in combination with advances in optimal convolution theory for the radio astronomy ``gridding'' problem. The theory behind this approach is explored, and a high performance implementation is presented for $w$-towers and Improved $w$-stacking within Improved $w$-towers.ARM Ltd iCase Sponsorshi

Multi-messenger astronomy in the era of gravitational wave detections

From the first detection of gravitational waves, to the discovery of the optical counterpart to a binary neutron star merger, gravitational-wave multi-messenger astronomy has been a powerful driving force in the development of new large-scale optical sky surveys, techniques, and methods, seeking to exploit the powerful synergies this new way of looking at the Universe has unlocked. This thesis is a compilation of original work from across time-domain astronomy – with a common thread of applying statistical methods to large datasets to extract new conclusions. Chapters 3 and 6 fuse deep learning and databases to build high-performance, uncertainty-aware source classification algorithms for large-scale optical sky surveys, breaking new ground in integrating contextual information directly into deep-learned classifiers. Chapter 4 constructs a Bayesian inference pipeline for homogeneous reprocessing of over 20 years of high-resolution spectra of the principal continuous-wave source and cornerstone LMXB, Sco X-1 – delivering the most precise ephemerides for the system thus far to enable high-sensitivity searches for gravitational waves. Chapter 5 presents a search for short- timescale variability in supernova light curves, with the aim of providing novel constraints on the structuring and density of the circumstellar medium in these systems. Although null results were obtained, the data constrain the amplitude of and rate of occurrence of previously-observed fluctuations, and allow us to develop the techniques necessary to extend this study to a larger sample in future

Expect the Unexpected: Deciphering Exoplanetary Signals with Machine Learning Techniques

The field of exoplanets has enjoyed unprecedented growth in the past decades, planets are being discovered at an exponential rate. With the launch of next-generation facilities in the coming decades, the arrival of high-quality spectroscopic data is expected to bring about yet another revolutionary change in our understanding of these remote worlds. The field has been actively developing tools to comprehend the large stream of incoming data, and among them, Machine Learning techniques are building up momentum as an alternative to conventional approaches. In this work, I developed methodologies to uncover potential biases in the interpretation of the exoplanetary atmosphere introduced during data analysis. I showed that naively combining observations from different instruments might lead to biased results, and in some extreme cases like WASP-96 b, it is impossible to com- bine observations. A new scheme of retrieval framework, namely the L - retrieval, holds the potential to detect incompatibility among different datasets by combining light-curve fitting with atmospheric radiative transfer modelling. This work also documents the application of ML techniques to two distinct fields of exoplanetary science: a planet signal detection pipeline for direct imaging data and a suite of diagnostic tools designed for the characterisation of exoplanets. In both approaches, I pioneered the integration of Explainable AI techniques to improve the reliability of the deep learning models. Initial successes of these novel methodologies have provided an exciting prospect to tackle upcoming challenges with the use of Artificial Intelligence. How- ever, significant work remains to progress these models from their current proof-of- concept stage to general application framework. In this thesis, I will discuss their current limitations, potential future, and the next steps required

Rubin Observatory LSST Transients and Variable Stars Roadmap

The Vera C. Rubin Legacy Survey of Space and Time holds the potential to revolutionize time domain astrophysics, reaching completely unexplored areas of the Universe and mapping variability time scales from minutes to a decade. To prepare to maximize the potential of the Rubin LSST data for the exploration of the transient and variable Universe, one of the four pillars of Rubin LSST science, the Transient and Variable Stars Science Collaboration, one of the eight Rubin LSST Science Collaborations, has identified research areas of interest and requirements, and paths to enable them. While our roadmap is ever-evolving, this document represents a snapshot of our plans and preparatory work in the final years and months leading up to the survey\u27s first light

Optical design study, testing and qualification of a Schwarzschild-Couder telescope for CTA and an assessment on the Intensity Interferometry capabilities with CTA

There is a growing common effort in the very high energy community towards the development of new research infrastructures to answer the fundamental questions of modern high-energy astrophysics and astroparticle physics. The Cherenkov Telescope Array Observatory (CTAO) is an international project aiming to deploy two separate arrays to observe the whole VHE sky between E = 20 GeV up to E = 300 TeV in a long term plan of about 30 years of operations. CTA is designed to increase the sensitivity by a factor 10 at 1 TeV, to enlarge the detection area, the angular resolution and the field of view over the facilities operating today. The observatory will be characterized by high flexibility, enhanced monitoring and deep survey capabilities, short time scale and simultaneous observations in multiple fields. This PhD thesis addresses the optical design study and testing of dual mirror Imaging Atmospheric Cherenkov Telescopes (IACTs) for the incoming CTAO. All of the IACTs facilities currently operating rely on single mirror solutions, which are mostly parabolic or Davies-Cotton optical designs, however there is a novel interest in the development of dual mirror configurations following the Schwarzschild-Couder optical design. This peculiar design, based on two highly aspherical mirrors promises wide-field, aplanatic telescopes characterized by small f-numbers and more compact structures. Dual mirror solutions allow use smaller camera pixels (3-6 mm) based on Silicon Photo Multiplier technology in substitution of the larger Photo Multiplier Tubes (1 inch) currently in use. The increased complexity in terms of optics manufacturing, replication and alignment is motivated from the attractive new capabilities of such configuration. In this context the Italian National Institute for Astrophysics (INAF) supported by the Italian Ministry of Education, University and Research (MIUR), is developing a small sized telescope prototype for CTA, named ASTRI, which is based upon the Schwarzschild-Couder optical design. The present work deals with the challenging realization of this optical configuration that has never been applied to IACTs. After two introductory chapters on the gamma-ray astronomy and the ASTRI optical design and its main subsystems (chapters 1 and 2), the performances of this system are compared with those of the other common wide-field telescopes in use for Cherenkov observations and for other applications in astrophysics (chapter 3). This comparative study is based on a commercial ray tracing software into which the optical designs of the envisaged telescopes are reproduced. Subsequently in chapter 4, an extended study of the ASTRI capabilities in relation to the performance and environmental requirements issued by CTA is presented in a detailed analysis of compliance supported by ray tracing simulations, finite element analysis and tolerance studies. In chapter 5 the work on the qualification tests of the secondary mirror gives an insight into the complexity of the Schwarzschild-Couder optics. The realization of this optical element is challenging in relation to currently available technologies, in particular concerning the cost requirements imposed by the CTA project. These constraints and the large sagitta of the mirror (190 mm) requires the use of the hot slumping technique in substitution of the cold slumping and diamond milling approaches usually used in the manufacturing of mirrors for Cherenkov applications. The results of a careful and extended test campaign on a mirror prototype have indicated that this manufacturing technique can provide a reliable engineering process of production for such large, highly aspherical optics. With a perspective on the science with future large telescopes as those provided by CTA, an assessment study upon the potentialities of the Intensity Interferometry (II) technique is carried out in chapter 6. In particular, a new kind of observation based on II is explored; the method aims to estimate the direct distance of the celestial objects. The order of magnitudes of the problem parameters space and the sensitivity that CTA and other future large observatories should achieve is estimated by means of numerical simulations. A short-term concept of experiment to assess the reliability of this new method is also discussed in relation to a pilot measurement that could be pursued with the state of the art technology

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

Particle Physics Reference Library

This second open access volume of the handbook series deals with detectors, large experimental facilities and data handling, both for accelerator and non-accelerator based experiments. It also covers applications in medicine and life sciences. A joint CERN-Springer initiative, the “Particle Physics Reference Library” provides revised and updated contributions based on previously published material in the well-known Landolt-Boernstein series on particle physics, accelerators and detectors (volumes 21A,B1,B2,C), which took stock of the field approximately one decade ago. Central to this new initiative is publication under full open access

Review of Particle Physics

The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances. The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings