An Introduction to Radio Astronomy

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1 An Introduction to Radio Astronomy Bernard F. Burke Massachusetts Institute of Technology and Francis Graham-Smith Jodrell Bank, University of Manchester CAMBRIDGE UNIVERSITY PRESS

2 Contents Preface Acknowledgements xii 1 INTRODUCTION The role of radio observations in astronomy Thermal and non-thermal processes Radiation processes and radio observations 5 2 RADIO TELESCOPES AS ANTENNAS Effective area, beamwidth and power gain Antenna temperature Electromagnetic waves Polarization: the Stokes parameters 15 3 SIGNAL DETECTION AND NOISE Gaussian random noise Band-limited noise Detection and integration Radiometer principles Radiometers in practice Spectrometry Cross-correlation radiometry: interferometry 34 4 SINGLE-APERTURE RADIO TELESCOPES Angular resolution Partially steerable telescopes Aperture distributions and beam patterns Feed systems Surface accuracy Millimetre and sub-millimetre telescopes Smoothing - the response to a sky brightness distribution 48 5 THE TWO-ELEMENT INTERFEROMETER The basic two-element interferometer 50

3 viii Contents 5.2 Interferometers with finite bandwidth Interferometers and finite source size Fourier transforms and the u,y-plane Practical considerations Very-long-baseline interferometry (VLBI) The interferometer in geodesy and astrometry Interferometry at millimetre wavelengths 66 6 APERTURE SYNTHESIS Interferometer arrays The spectral sensitivity function Filling the u, u-plane Unfilled w.d-planes - VLA and MERLIN VLBI imaging Calibration of interferometer data Synthesis imaging Self-calibration Aperture synthesis at millimetre wavelengths 84 7 THE ABSORPTION, AMPLIFICATION, REFRACTION AND ATTENUATION OF RADIO WAVES Radiative transfer Masers Propagation through ionized gas Faraday rotation Scintillation Propagation in the Earth's atmosphere 93 8 GALACTIC CONTINUUM RADIATION Stars, dust and gas Varieties of galaxies Measurement of antenna temperature The spectrum of the galactic continuum Cosmic rays and the magnetic field of the Galaxy Synchrotron radiation Polarization and Faraday rotation Loops and spurs The Local Bubble Other galaxies THE INTERSTELLAR MEDIUM Temperature states of the ISM Line formation in the ISM 119

4 Contents ix 9.3 Neutral hydrogen (HI) Ionized hydrogen (HII) The hot ionized component Heating and cooling mechanisms Dense molecular clouds Radio molecular lines Supernova remnants (SNR) Dark matter GALACTIC DYNAMICS Atoms and molecules in the Milky Way The circular approximation Spiral structure Strong non-circular motions The galactic centre The distribution of matter The scale of the Galaxy STARS Surface brightness The Sun and planets Circumstellar masers The silicon oxide masers The water masers The hydroxyl masers Classical novae Non-thermal radiation from binaries and flare stars Recurrent novae X-ray binaries - Cyg X-3 and SS PULSARS Neutron star structure Rotational slowdown Radio and optical emission from pulsars The radiation mechanism The population and evolution of pulsars Binary orbits and interactions Tests of general relativity RADIO GALAXIES AND QUASARS Spectra and dimensions Structures A simple model of active galactic nuclei 208

5 x Contents 13.4 The accretion disk The torus The core and the jets Spectra of quasars and other AGNs The radio brightness temperature of the core Superluminal motion The radio jets and lobes Radio galaxies with low luminosity COSMOLOGY AND THE COSMIC MICROWAVE BACKGROUND The Hubble flow A simple Newtonian model Relativistic cosmology Big Bang cosmology The cosmic microwave background Anisotropy and distortions of the CMB The inflation theory COSMOLOGY: DISCRETE RADIO SOURCES AND GRAVITATIONAL LENSES Evolution and the radio source counts Angular diameters Gravitational lensing Observations of lenses: rings, quads and others Time delay THE PLACE OF RADIO IN ASTRONOMY The cosmic microwave background The interstellar medium Angular resolution: stars and quasars The protection of radio frequencies in astronomy 259 Appendix 1 Fourier transforms 261 Appendix 2 Celestial Coordinates, Distance and Time 268 Appendix 3 The Origins of Radio Astronomy 21A References and Recommended Reading 280 Index 295

An Introduction to Radio Astronomy

An Introduction to Radio Astronomy Second edition Bernard F. Burke and Francis Graham-Smith CAMBRIDGE UNIVERSITY PRESS Contents Preface to the second edition page x 1 Introduction 1 1.1 The role of radio