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 observations in astronomy 1 1.2 Thermal and non-thermal processes 4 1.3 Radiation processes and radio observations 6 2 Radio telescopes as antennas 8 2.1 Beamwidth, effective area and the jansky 8 2.2 Antenna temperature 10 2.3 Electromagnetic waves 13 2.4 Polarization: the Stokes parameters 16 3 Signal detection and noise 21 3.1 Gaussian random noise V 21 3.2 Band-limited noise 23 3.3 Detection and integration 25 3.4 Radiometer principles 27 3.5 Radiometers in practice 30 3.6 Spectrometry 34 3.7 Cross-correlation radiometry: interferometry 38 4 Single-aperture radio telescopes 40 4.1 Angular resolution 40 4.2 Steerable radio telescopes 42 4.3 Phased arrays 42 4.4 Aperture distributions and beam patterns 44 4.5 Feed systems 48 4.6 Surface accuracy 51 4.7 Millimetre and sub-millimetre telescopes 53
vi Contents 4.8 Smoothing: the response to a sky brightness distribution 54 5 The two-element interferometer 56 5.1 The basic two-element interferometer 57 5.2 Interferometers with finite bandwidth 61 5.3 Interferometers and finite source size 63 5.4 Fourier transforms and the u,v-plane 65 5.5 Practical considerations 67 5.6 Very-long-baseline interferometry (VLBI) 69 5.7 Beam switching 73 5.8 The interferometer in geodesy and astrometry 74 5.9 Interferometry at millimetre wavelengths 75 5.10 Optical interferometry 77 6 Aperture synthesis 79 6.1 Interferometer arrays 80 6.2 The spectral sensitivity function 82 6.3 Filling the u,v-plane 85 6.4 Frequency diversity 90 6.5 Wide fields and wide bandwidths 90 6.6 Synthesis imaging 92 6.7 VLBI arrays 94 6.8 Calibration of interferometer data 96 6.9 Self-calibration 97 6.10 Signal-to-noise limitations and dynamic range 99 6.11 Aperture synthesis at millimetre wavelengths 102 6.12 Space VLBI 103 7 Radiation, propagation and absorption of radio waves 104 7.1 Radiative transfer 105 7.2 Synchrotron radiation 106 7.3 A power-law energy distribution 110 7.4 Synchrotron self-absorption 113 7.5 Free-free radiation 113 7.6 Radio spectral lines 116 7.7 Masers 118 7.8 Propagation through ionized gas 120 7.9 Faraday rotation 121 7.10 Scintillation 123 7.11 Propagation in the Earth's atmosphere 125
Contents vii 8 Galactic continuum radiation 128 8.1 Stars, dust and gas 129 8.2 Varieties of galaxies 132 8.3 Measurement of sky brightness temperature 133 8.4 The spectrum of the Galactic continuum 134 8.5 Synchrotron radiation: emissivity 137 8.6 The energy spectrum of cosmic rays 139 8.7 Polarization 141 8.8 Faraday rotation: the Galactic magnetic field 142 8.9 Loops and spurs 148 8.10 The Local Bubble 150 8.11 Other galaxies 151 9 The interstellar medium 153 9.1 Temperature states of the ISM 153 9.2 9.3 9.4 9.5 9.6 9.7 9.8 Neutral hydrogen (H I) Ionized hydrogen (H II) The hot ionized component Heating and cooling mechanisms Dense molecular clouds Radio molecular lines Supernova remnants (SNRs) 10 Galactic dynamics 10.1 Atoms and molecules in the Milky Way 10.2 The circular approximation 10.3 Spiral structure 10.4 Non-circular motions 10.5 The distribution of matter 10.6 The Galactic Centre 10.7 The scale of the Galaxy 11 Stan 11.1 11.2 11.3 11.4 11.5 11.6 11.7 Surface brightness The Sun The planets Circumstellar envelopes Circumstellar masers The silicon oxide masers The water masers 154 159 162 162 164 165 167 175 176 179 183 188 193 197 201 205 205 208 211 215 217 218 218
viii Contents 11.8 The hydroxyl masers 219 11.9 Classical novae 221 11.10 Non-thermal radiation from binaries and flare stars 226 11.11 Recurrent novae 228 11.12 X-ray binaries: Cyg X-3 and SS 433 229 11.13 Superluminal motion 230 12 Pulsars 236 12.1 Neutron stars 236 12.2 Neutron star structure 237 12.3 Rotational slowdown 239 12.4 Rotational behaviour of the Crab and Vela pulsars 240 12.5 Superfluid rotation 243 12.6 Radio and optical emission from pulsars 246 12.7 The radiation mechanism 251 12.8 The population and evolution of pulsars 253 12.9 Searches and surveys; the constraints 255 12.10 Trigonometric distance and proper motion 258 12.11 X-ray pulsars 259 12.12 Magnetic dipole moments 260 12.13 Binary orbits and interactions 263 12.14 Tests of general relativity 265 13 Radio galaxies and quasars 268 13.1 Radio emission from normal galaxies 270 13.2 Spectra and dimensions 272 13.3 Structures 273 13.4 A simple model of active galactic nuclei 279 13.5 The accretion disc 281 13.6 The torus 282 13.7 The core and the jets 284 13.8 Spectra of quasars and other AGNs 287 13.9 The radio brightness temperature of the core 289 13.10 Superluminal motion 290 13.11 The radio j ets and lobes 292 13.12 The kiloparsec scale radio sources 293 14 Cosmology and the cosmic microwave background 296 14.1 The Hubble flow 297 14.2 A simple Newtonian model 298 14.3 Relativistic cosmology 301
Contents 14.4 Two fundamental problems of cosmology 303 14.5 Big Bang cosmology 305 14.6 The cosmic microwave background 308 14.7 Anisotropy and distortions of the CMB 311 15 Cosmology: discrete radio sources and gravitational lenses 318 15.1 Evolution and the radio source counts 318 15.2 Angular diameter and expansion velocity 324 15.3 Gravitational lensing 326 15.4 Observations of lenses: rings, quads and others 333 15.5 Weak gravitational imaging 337 15.6 Time delay 340 16 The place of radio in astronomy 341 16.1 The cosmic microwave background 342 16.2 The interstellar medium 343 16.3 Angular resolution: stars and quasars 344 16.4 Future developments 346 16.5 The protection of radio frequencies in astronomy 347 Appendices 351 Appendix 1 Fourier transforms 351 A 1.1 Definitions 351 A1.2 Convolution and cross-correlation 355 A1.3 Two or more dimensions 358 Appendix 2 Celestial coordinates, distance and time 360 A2.1 The celestial coordinate system 360 A2.2 The astronomical distance scale 363 A2.3 Time 364 Appendix 3 The origins of radio astronomy 367 References 374 Index 389 ix