An Introduction to Radio Astronomy 4Th Edition Bernard F

Cambridge University Press 978-1-107-18941-6 — An Introduction to Radio Astronomy 4th Edition Bernard F. Burke , Francis Graham-Smith , Peter N. Wilkinson Frontmatter More Information

AN INTRODUCTION TO RADIO ASTRONOMY

Fourth Edition

Radio astronomy is an active and rapidly expanding field owing to advances in computing techniques, with several important new instruments on the horizon. This text provides a thorough introduction to radio astronomy and its contribution to our understanding of the Universe, bridging the gap between basic introductions and research-level treatments. It begins by covering the fundamental physics of radio techniques, before moving on to single-dish telescopes and aperture-synthesis arrays. Fully updated and extensively rewrit- ten, this Fourth Edition places greater emphasis on techniques, with a detailed discussion of interferometry in particular and an introduction to digital techniques in the appendices. The science sections have been fully revised, with new author Peter Wilkinson bringing added expertise to the sections on quasars and active galaxies. Spanning the entirety of radio astronomy, this is an engaging introduction for students and researchers approaching radio astronomy for the first time. bernard f. burke was William A. M. Burden Professor of Astrophysics, formerly of the Radio Astronomy Group of the MIT Research Laboratory of Electronics, and prin- cipal investigator at the MIT Kavli Institute for Astrophysics and Space Research. He was elected a member of the United States National Academy of Sciences in 1970 and served as AAS President from 1986 to 1988. He and Kenneth Franklin discovered that Jupiter is a source of radio waves while working at the Carnegie Institution for Science, and he was part of the six-member team credited with the discovery in 1988 of the first Einstein ring. sir francis graham-smith, frs is Emeritus Professor at the University of Manchester. He was Astronomer Royal from 1982 to 1990 and Director of Jodrell Bank Observatory between 1981 and 1988. As Director of the Royal Greenwich Observatory between 1975 and 1981, Graham-Smith instituted the UK optical observatory on La Palma. In his student days at Cambridge he made the first accurate locations of cosmic radio sources, leading to their identification. At Jodrell Bank he discovered radio emission from cosmic ray showers and continues to work on pulsars, in which he discovered the polarization of the radio pulses. He is a co-author of Pulsar Astronomy (Cambridge University Press, Fourth Edition 2012). peter n. wilkinson is Emeritus Professor of Radio Astronomy at the University of Manchester. He has been involved in the development of radio telescopes at Jodrell Bank Observatory since 1967, including five years spent jointly at the California Institute of Technology and the US National Radio Astronomy Observatory. In 1991 he wrote the first published paper describing the scientific rationale and outline structure of a radio interferometer array, which developed into the Square Kilometre Array (SKA) project. He is now working on a novel radio telescope to map the sky with a precision ten times better than that achieved by the discoverers of the cosmic microwave background. He is a leading member of the UK’s Newton DARA Project, which teaches radio astronomy to students in Africa in preparation for hosting part of the Square Kilometre Array.

© in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-1-107-18941-6 — An Introduction to Radio Astronomy 4th Edition Bernard F. Burke , Francis Graham-Smith , Peter N. Wilkinson Frontmatter More Information

AN INTRODUCTION TO RADIO ASTRONOMY Fourth Edition

BERNARD F. BURKE Massachusetts Institute of Technology

FRANCIS GRAHAM-SMITH University of Manchester

PETER N. WILKINSON University of Manchester

University Printing House, Cambridge CB2 8BS, United Kingdom One Liberty Plaza, 20th Floor, New York, NY 10006, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia 314-321, 3rd Floor, Plot 3, Splendor Forum, Jasola District Centre, New Delhi - 110025, India 103 Penang Road, #05-06/07, Visioncrest Commercial, Singapore 238467

Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781107189416 DOI: 10.1017/9781316987506 © Bernard F. Burke, Francis Graham-Smith and Peter N. Wilkinson 2019 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 1996 Second edition 2002 Third edition 2010 Fourth edition 2019 A catalogue record for this publication is available from the British Library Library of Congress Cataloging in Publication data Names: Burke, Bernard F., 1928- author. | Graham-Smith, Francis, 1923- author. | Wilkinson, Peter N., 1946- author. Title: An introduction to radio astronomy / Bernard F. Burke (Massachusetts Institute of Technology), Francis Graham-Smith (University of Manchester), Peter N. Wilkinson (University of Manchester). Description: Fourth edition. | Cambridge, United Kingdom ; New York, NY : Cambridge University Press, 2019. | Includes bibliographical references and index. Identifiers: LCCN 2018057974 | ISBN 9781107189416 (hardback ; alk. paper) | ISBN 1107189411 (hardback ; alk. paper) Subjects: LCSH: Radio astronomy–Observations. | Radio astronomy–Methodology. Classification: LCC QB476.5 .B87 2019 | DDC 522/.682–dc23 LC record available at https://lccn.loc.gov/2018057974 ISBN 978-1-107-18941-6 Hardback Additional resources for this publication at www.cambridge.org/ira4 Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

In memoriam Our dear friend and colleague Bernard Burke died on 5 August 2018. He was co-author of the ﬁrst edition of this Introduction in 1996. His own introduction to radio astronomy was in 1953, with FG-S at the Carnegie Institution of Washington. Bernie was known for his deep physical understanding, his good humour, and his love of history. He was widely consulted and gave wise advice on many projects in astronomy.

Contents

Preface page xvii

Part I The Emission, Propagation, and Detection of Radio Waves 1 The Role of Radio Observations in Astronomy 3 1.1 The Discovery of Cosmic Radio Waves 3 1.2 The Origins of Radio Astronomy 6 1.3 Thermal and Non-Thermal Radiation Processes 8 1.4 Radio Observations 10 1.5 The Challenge of Manmade Radio Signals 12 1.6 Further Reading 14 2 Emission and General Properties of Radio Waves 15 2.1 Electromagnetic Waves 15 2.2 Wave Polarization 17 2.2.1 The Polarization Ellipse 18 2.3 Blackbody Radiation 21 2.4 Speciﬁc Intensity and Brightness 24 2.5 Radiative Transfer 26 2.6 Free–Free Radiation 29 2.7 Synchrotron Radiation 32 2.7.1 A Power-Law Energy Distribution 36 2.7.2 Synchrotron Self-Absorption 38 2.8 Inverse Compton Scattering 39 2.9 Further Reading 40 3 Spectral Lines 41 3.1 Radio Recombination Lines 42 3.2 Hyperﬁne Atomic Ground-State Transitions 44 3.3 Rotational Lines 45 3.4 Degeneracy Broken by Rotation 47 3.5 Detected Lines 49 3.6 Linewidths 50 3.6.1 Line Emission and Absorption 51

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3.7 Masers 53 3.7.1 Common Masers 56 3.8 Further Reading 57 4 Radio Wave Propagation 58 4.1 Refractive Index 58 4.1.1 Dispersion and Group Velocity 59 4.2 Faraday Rotation 60 4.3 Scintillation 62 4.4 Propagation in the Earth’s Atmosphere 65 4.5 Further Reading 68 5 The Nature of the Received Radio Signal 69 5.1 Gaussian Random Noise 69 5.2 Brightness Temperature and Flux Density 71 5.2.1 Brightness Temperatures of Astronomical Sources 75 5.3 Antenna Temperature 76 5.3.1 Adding Noise Powers 78 5.3.2 Sources of Antenna Noise 79 5.3.3 Measuring the Antenna Temperature 80 5.4 Further Reading 81 6 Radiometers 82 6.1 The Basic Radiometer 83 6.1.1 Impedance Matching and Power Transfer 83 6.1.2 Power Ampliﬁcation 84 6.1.3 Bandwidth and Coherence 84 6.2 Detection and Integration 85 6.3 Post-Detection Signals 87 6.3.1 Time Series 87 6.3.2 Spectrum 89 6.3.3 Recognizing a Weak Source 90 6.4 System Noise Temperature 91 6.4.1 Receiver Temperature 91 6.4.2 Receivers for Millimetre and Sub-Millimetre Waves 93 6.4.3 System Equivalent Flux Density (SEFD) 94 6.5 Calibration of the System Noise 95 6.5.1 Receiver Noise Calibration 95 6.5.2 Secondary Methods 96 6.5.3 Relative and Absolute Calibration 97 6.6 Heterodyne Receivers 97 6.7 Tracing Noise Power through a Receiver 100 6.8 Gain Variations and Their Correction 101 6.8.1 Dicke Switched Radiometer 103 6.8.2 Correlation Radiometers 105 6.9 Digital Techniques 107 6.10 Further Reading 107

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7 Spectrometers and Polarimeters 108 7.1 Spectrometers 108 7.1.1 Filter-Bank Spectrometers 109 7.2 Autocorrelation Spectrometers 110 7.2.1 Linewidth and the Window Function 112 7.3 Digital Autocorrelation Spectrometers 115 7.3.1 Fast Fourier Transform Spectrometers 116 7.4 Polarimetry 118 7.5 Stokes Parameters 118 7.5.1 Choice of Orthogonal Polarizations 122 7.6 Polarized Waveguide Feeds 124 7.6.1 Linear Feeds and Quadrature Hybrids 125 7.7 A Basic Polarimeter 125 7.8 Practical Considerations 126 7.9 Further Reading 127

Part II Radio Telescopes and Aperture Synthesis 8 Single-Aperture Radio Telescopes 131 8.1 Fundamentals: Dipoles and Horns 131 8.1.1 Ground Planes 135 8.1.2 The Horn Antenna 136 8.1.3 Wide-Band Antennas 138 8.2 Phased Arrays of Elementary Antennas 139 8.3 Antenna Beams 145 8.3.1 Aperture Distributions and Beam Patterns 146 8.3.2 Fraunhofer Diffraction at an Aperture 147 8.3.3 Effective Area 151 8.4 Partially Steerable Telescopes 153 8.5 Steerable Telescopes 154 8.6 Feed Systems 156 8.6.1 Twin-Beam Radiometry 158 8.7 Focal Plane Arrays and Phased Array Feeds 159 8.8 Antenna Efﬁciency 160 8.8.1 Aperture Illumination 160 8.8.2 Blockage of the Aperture 162 8.8.3 Reﬂection at the Surface 163 8.8.4 Summary 165 8.9 The Response to a Sky Brightness Distribution 166 8.9.1 Beam Smoothing and Convolution 166 8.9.2 Sampling in Angle 170 8.9.3 Effects of Sidelobes 170 8.9.4 Pointing Accuracy 171 8.9.5 Source Confusion 172

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8.9.6 Source Positions 172 8.10 State-of-the-Art Radio Telescopes 173 8.10.1 FAST and Arecibo 174 8.10.2 Large Steerable Dishes with Active Surfaces 174 8.10.3 Millimetre and Sub-Millimetre Wave Dishes 175 8.11 Further Reading 175 9 The Basics of Interferometry 177 9.1 The Basic Two-Element Interferometer 178 9.1.1 One-Dimensional Geometry 180 9.1.2 The Adding Interferometer 181 9.1.3 The Correlation Interferometer 182 9.1.4 Steps Towards Practicality 185 9.1.5 The Frequency Domain Approach 186 9.2 Finite Bandwidths and Fields of View 187 9.3 The Basis of Position Measurements 189 9.4 Dealing with Finite Source Sizes 192 9.4.1 The Situation in One Dimension 192 9.4.2 The Essence of Fourier Synthesis 196 9.4.3 Simple Sources and their Visibility Amplitudes 197 9.5 Interferometry in Two Dimensions 200 9.5.1 Coordinate-Free Description 201 9.5.2 The u, v Plane and the 2D Fourier Transform 202 9.6 Coherence 207 9.7 Propagation Effects 210 9.7.1 Troposphere 211 9.7.2 Ionosphere 212 9.8 Practical Considerations 214 9.8.1 Point-Source Sensitivity 214 9.8.2 Amplitude and Phase Calibration: Basic Ideas 215 9.8.3 Outline of a Practical Signal Path 217 9.9 Further Reading 219 10 Aperture Synthesis 220 10.1 Interferometer Arrays 220 10.2 Recapitulation on the Visibility Function 224 10.3 The Data from an Array 224 10.4 Conditions for a 2D Fourier Transform 225 10.5 The Spatial Frequency Transfer Function, or u, v Coverage 227 10.6 Filling the u, v Plane 229 10.6.1 The u, v Coverage and Earth Rotation 229 10.6.2 The Effect of Incomplete u, v Coverage 236 10.7 Calibrating the Data 238 10.7.1 Flux and Bandpass Calibration 239 10.7.2 Amplitude Calibration 239 10.7.3 Phase Calibration 240

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10.8 Producing the Initial Map 242 10.8.1 Gridding and Weighting the Data 242 10.8.2 Dimensions in the Image and the Visibility Planes 244 10.9 Non-Linear Deconvolution 245 10.9.1 The CLEAN Algorithm 246 10.10 Correcting the Visibility Data 249 10.10.1 Closure Quantities 249 10.10.2 Self-Calibration 251 10.11 Missing Short Spacings 254 10.12 Flux Density and Brightness Sensitivity 254 10.12.1 Source Confusion 258 10.13 Multifrequency Synthesis 258 10.14 Data Limitations 259 10.14.1 Flagging 259 10.14.2 Time Averaging 260 10.14.3 Frequency Averaging 260 10.14.4 Non-Closing Effects 261 10.15 Image Quality 262 10.15.1 Signal-to-Noise Limits 262 10.15.2 Dynamic Range 263 10.15.3 Fidelity 264 10.16 Further Reading 265 11 Further Interferometric Techniques 266 11.1 Spectral Line Imaging 266 11.1.1 Observational Choices 267 11.1.2 Data Analysis Issues 268 11.2 Polarization Imaging 269 11.2.1 Basic Formalism 269 11.2.2 Calibration for Linear Polarization 270 11.3 Aperture Synthesis at Millimetre Wavelengths 273 11.3.1 Phase and Amplitude Calibration 274 11.3.2 System Requirements and Current Arrays 275 11.4 Very Long Baseline Interferometry (VLBI) 277 11.4.1 VLBI versus Connected-Element Interferometry 277 11.4.2 Outline of a VLBI System 278 11.4.3 Amplitude Calibration 280 11.4.4 Delay and Phase Corrections; Fringe Fitting 280 11.4.5 Basic VLBI Analysis for Imaging 282 11.4.6 Geodesy and Astrometry 283 11.4.7 Methods 283 11.4.8 Astrometry 285 11.4.9 Geodesy 286 11.4.10 Space VLBI 287 11.4.11 VLBI Arrays 288

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11.5 Wide-Field Imaging 288 11.5.1 The w-term and its Effects 289 11.5.2 Effects of the Primary Beam 291 11.5.3 Peeling 292 11.5.4 Mosaicing 292 11.6 Low Frequency Imaging 294 11.6.1 The Challenges 295 11.6.2 Low Frequency Arrays 297 11.7 Further Reading 298

Part III The Radio Cosmos 12 The Sun and the Planets 301 12.1 Surface Brightness of the Quiet Sun 301 12.2 Solar Radio Bursts 303 12.3 Coronal Mass Ejection (CME) 306 12.4 The Planets 307 12.5 Further reading 308 13 Stars and Nebulae 309 13.1 Thermal Radio Emission from Stars 309 13.2 Circumstellar Envelopes 312 13.3 Circumstellar Masers 313 13.3.1 Silicon Oxide 314 13.3.2 Methanol 314 13.3.3 Water 315 13.4 The Hydroxyl Masers 315 13.5 Classical Novae 318 13.6 Recurrent Novae 320 13.7 Non-Thermal Radiation from Binaries and Flare Stars 324 13.8 X-Ray Binaries and Microquasars 324 13.9 Superluminal Motion 325 13.10 H II Regions 329 13.11 Supernova Remnants 331 13.12 Further Reading 337 14 The Milky Way Galaxy 338 14.1 The Structure of the Galaxy 338 14.2 Galactic Rotation: The Circular Approximation 342 14.3 Spiral Structure 345 14.4 The Galactic Centre Region 349 14.5 The Black Hole at the Galactic Centre 351 14.6 The Spectrum of the Galactic Continuum 352 14.7 Synchrotron Radiation: Emissivity 355 14.8 The Energy Spectrum of Cosmic Rays 356 14.9 Polarization of the Galactic Synchrotron Radiation 357

Contents xiii

14.10 Faraday Rotation: the Galactic Magnetic Field 359 14.11 Loops and Spurs 363 14.12 The Local Bubble 365 14.13 Further Reading 366 15 Pulsars 367 15.1 Neutron Stars 367 15.1.1 Neutron Star Structure 368 15.2 Rotational Slowdown 369 15.3 Magnetic Dipole Moments 371 15.4 Rotational Behaviour of the Crab Pulsar 371 15.5 Glitches in Other Pulsars 373 15.5.1 Superﬂuid Rotation 373 15.6 Radio, Optical, X-Ray, and Gamma-Ray Emission from the Magnetosphere 374 15.7 Polar Cap Radio Emission 376 15.7.1 Polarization 377 15.7.2 Individual and Integrated Pulses 379 15.7.3 Nulling, Moding, and Timing Noise 380 15.8 Magnetars 381 15.9 X-Ray Binaries and Millisecond Pulsars 383 15.10 Binary Millisecond Pulsars 384 15.10.1 Gamma-Ray Pulsars 384 15.11 The Population and Evolution of Pulsars 386 15.12 The Radiation Mechanism 387 15.13 Pulsar Timing 388 15.14 Distance and Proper Motion 390 15.15 Binary Radio Pulsars 390 15.15.1 The Analysis of Binary Orbits 391 15.15.2 Post-Keplerian Analysis 392 15.16 Searches and Surveys: The Constraints 394 15.17 Detecting Gravitational Waves 395 15.18 Further Reading 396 16 Active Galaxies 397 16.1 Star-Forming Galaxies 397 16.2 Active Galactic Nuclei 401 16.3 Radio-Loud AGN 402 16.3.1 Classiﬁcation of Extended Radio Sources 402 16.3.2 FR II Sources 403 16.3.3 FR I Sources 405 16.3.4 Core–Jet Sources 407 16.3.5 Repeated Outbursts 407 16.3.6 Synchrotron Emission from Extended Sources 409 16.3.7 Sub-Galactic-Scale Radio Sources 411

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16.3.8 Compact Radio Sources 412 16.3.9 Superluminal Motion 414 16.3.10 Brightness Temperatures in Compact Sources 415 16.4 Other Properties of Radio-Loud AGN 416 16.4.1 Optical Emission Lines 416 16.4.2 Spectral Energy Distributions (SEDs) 417 16.4.3 Variability 417 16.4.4 Host Galaxies and SMBHs 419 16.5 Uniﬁed Models of Radio-Loud AGN 420 16.5.1 Radiative-Mode AGN 420 16.5.2 Kinetic-Mode AGN 426 16.6 Accretion Rates and Feedback 427 16.7 Radio-Quiet AGN 429 16.8 Summary of AGN Phenomenology 430 16.9 Surveys, Source Counts, and Evolution 431 16.9.1 Early Source Counts 431 16.9.2 Modern Source Surveys 433 16.9.3 Modern Source Counts 435 16.9.4 Evolution of Source Populations 437 16.9.5 Future Continuum-Source Surveys 438 16.10 Further Reading 440 17 The Radio Contributions to Cosmology 441 17.1 The Expanding Cosmos 441 17.2 A Brief History 441 17.3 Geometry and Dynamics 442 17.4 The Early Universe: The CMB 445 17.5 The Cosmic Dipole: The Coordinate Frame of the Universe 447 17.6 The Blackbody Spectrum of the CMB 447 17.7 The Search for Structure 448 17.7.1 First Observations of Structure 450 17.7.2 Wilkinson Microwave Anisotropy Probe (WMAP) 451 17.7.3 Planck 452 17.7.4 South Pole Telescope 453 17.8 The Derivation of Cosmological Quantities 454 17.9 Polarization Structure of the CMB 455 17.10 The Transition to the Era of Reionization 457 17.11 The Sunyaev–Zel’dovich Effect 458 17.12 Gravitational Lensing 461 17.13 Ray Paths in a Gravitational Lens 462 17.13.1 Imaging by Extended Lenses 464 17.14 Lensing Time Delay 465 17.15 Weak Gravitational Imaging 465 17.16 Further Reading 466

Contents xv

Appendix 1 Fourier Transforms 467 A1.1 Deﬁnitions 467 A1.2 Convolution and Cross-Correlation 470 A1.3 Two or More Dimensions 474 A1.4 Further Reading 474 Appendix 2 Celestial Coordinates and Time 475 A2.1 The Celestial Coordinate System 475 A2.2 Time 477 A2.3 Further Reading 479 Appendix 3 Digitization 480 A3.1 Digitizing the Signal 480 A3.1.1 Amplitude Quantization 480 A3.1.2 Time Quantization and the Nyquist Criterion 482 A3.1.3 Aliassing 483 Appendix 4 Calibrating Polarimeters 487 A4.1 Single-Dish Radio Telescopes 487 A4.2 Polarization in Interferometers 488 A4.3 Further Reading 490 Appendix 5 Spherical Harmonics 491

References 493 Index 517

Preface

Astronomy makes use of more than 20 decades of the electromagnetic spectrum, from gamma-rays to radio. The observing techniques vary so much over this enormous range that there are distinct disciplines of gamma-ray, X-ray, ultraviolet, optical, infrared, millimetre, and radio astronomy. Modern astrophysics depends on a synthesis of observations from the whole wavelength range, and the concentration on radio in this text needs some rationale. Apart from the history of the subject, which developed from radio communications rather than as a deliberate extension of conventional astronomy, there are two outstanding characteristics of radio astronomy which call for a special exposition. First, the astrophysics. Radio is essential for observing: – ionized atmospheres of stars and interstellar plasma, penetrating dust and gas which often obscure other wavelengths; – the processes of star and planet formation; – molecules in cold interstellar clouds; – hydrogen, the fundamental element in the Universe; – pulsars, the most accurate clocks in the Universe; – cosmic magnetic ﬁelds; – the structure of the early cosmos.

Second, the techniques: low energy radio photons can be treated as classical waves. Hence, in contrast with other regimes, they can be coherently amplified and manipulated in complex receiver systems. Coherent amplification enables one to take account of the phase as well as the intensity of incoming waves, allowing the development of interferometers with the highest angular resolution in astronomy and the development of aperture synthesis, now realized in powerful new interferometric radio telescopes such as LOFAR, LWA, MeerKAT, MWA, ASKAP and ALMA, with the first phase of the Square Kilometre Array (SKA) impending. The basic techniques follow well-established principles, but the advent of massive computer power and broadband fibre optic communications has only recently brought these impressive instruments within the range of possibility. At the same time, existing radio telescopes, now including the new five-hundred metre FAST, using new receiver technology continue front-line research in several astrophysical domains, such as pulsars, fast radio bursts, and large area surveys for low-brightness emission. Fundamental cosmology has been transformed by observations of the cosmic microwave background from spacecraft and from the ground.

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In view of the developments in the last ten years, this fourth edition of the book has been completely revised and reorganized. The new generation of radio telescopes, with dramat- ically improved performance, and new generations of astronomers, require a presentation which is a combination of fundamental principles, an exposition of the basics of telescope techniques, and a survey of the radio cosmos. Our rewriting has followed the advice of many colleagues, and we have provided references to recent reviews as well as to papers which represent the current state of the art. We are also providing on-line supplementary material, presenting a wide range of colour images and other material to complement the text. It will be available at www.cambridge.org/ira4. We are aiming particularly at a graduate student audience attracted by radio astronomy with its new observational capabilities – in particular SKA, which will grow in size and power over the next two decades. For the reader wishing to progress further in the subject there is a growing list of books at a more advanced level. Of these we particularly recommend: Interferometry and Synthesis in Radio Astronomy, A. R. Thompson, J. M. Moran, and G. W. Swenson (Springer). Essential Radio Astronomy, J. J. Condon and S. M. Ransom (Princeton University Press). Tools of Radio Astronomy, T. L. Wilson, K. Rohlfs, and S. Huttemeister¨ (Springer). Our intention is to provide an introduction which is useful both to the observer and to the astrophysicist; perhaps it will appeal most to those who, like ourselves, enjoy the membership of both categories

Acknowledgements

We have gained many insights from the three books listed in the preface. In our treatment of interferometry we have made extensive use of tutorial presentations in the proceedings of: (i) the NRAO synthesis imaging workshops; (ii) the European Radio Interferometry Schools (ERIS), (iii) the CSIRO astronomy and space science (CASS) radio astronomy schools, all of which are available on the web. The introductory presentations by Rick Per- ley were particularly helpful. We also acknowledge pedagogic insights from Tim Bastian, Wim Brouw, Ger de Bruyn, John Conway, Tim Cornwell, Darrell Emerson, Andre´ Fletcher, Mike Garrett, Simon Garrington, Neal Jackson, Hans-Rainer Klockner,¨ Robert Laing, Ray Norris, Tetsuo Sasao, and David Wilner. The videos by Aaron Parsons on the ‘Astrobaki’ website1 are highly recommended. We are grateful to Clive Tadhunter for permission to reproduce Figure 16.16. Colleagues at the University of Manchester’s Jodrell Bank Centre for Astrophysics have read critically parts of the text, contributed original diagrams, or offered astronomical and technical insights – sometimes all three! They are: Adam Avison, Rob Beswick, Ian Browne, Clive Dickinson, Malcolm Gray, Neal Jackson, Scott Kay, Paddy Leahy,

1 casper.berkeley.edu/astrobaki/index.php/Radio Astronomy: Tools and Techniques.

Preface xix

Ian Morison, Tom Muxlow, Anita Richards, Ralph Spencer, Peter Thomasson, Patrick Weltevrede, Althea Wilkinson, and Nick Wrigley. Finally we are indebted to Christine Jordan for guiding FG-S through the intricacies of his LaTeX set-up and for assembling the text of this book. Bernard F. Burke Francis Graham-Smith Peter N. Wilkinson