An Introduction to Radio Astronomy

Transcription

1 An Introduction to Radio Astronomy Second edition Bernard F. Burke and Francis Graham-Smith CAMBRIDGE UNIVERSITY PRESS

2 Contents Preface to the second edition page x 1 Introduction The role of radio observations in astronomy Thermal and non-thermal processes Radiation processes and radio observations 6 2 Radio telescopes as antennas Beamwidth, effective area and the jansky Antenna temperature Electromagnetic waves Polarization: the Stokes parameters 16 3 Signal detection and noise Gaussian random noise V Band-limited noise Detection and integration Radiometer principles Radiometers in practice Spectrometry Cross-correlation radiometry: interferometry 38 4 Single-aperture radio telescopes Angular resolution Steerable radio telescopes Phased arrays Aperture distributions and beam patterns Feed systems Surface accuracy Millimetre and sub-millimetre telescopes 53

3 vi Contents 4.8 Smoothing: the response to a sky brightness distribution 54 5 The two-element interferometer The basic two-element interferometer Interferometers with finite bandwidth Interferometers and finite source size Fourier transforms and the u,v-plane Practical considerations Very-long-baseline interferometry (VLBI) Beam switching The interferometer in geodesy and astrometry Interferometry at millimetre wavelengths Optical interferometry 77 6 Aperture synthesis Interferometer arrays The spectral sensitivity function Filling the u,v-plane Frequency diversity Wide fields and wide bandwidths Synthesis imaging VLBI arrays Calibration of interferometer data Self-calibration Signal-to-noise limitations and dynamic range Aperture synthesis at millimetre wavelengths Space VLBI Radiation, propagation and absorption of radio waves Radiative transfer Synchrotron radiation A power-law energy distribution Synchrotron self-absorption Free-free radiation Radio spectral lines Masers Propagation through ionized gas Faraday rotation Scintillation Propagation in the Earth's atmosphere 125

4 Contents vii 8 Galactic continuum radiation Stars, dust and gas Varieties of galaxies Measurement of sky brightness temperature The spectrum of the Galactic continuum Synchrotron radiation: emissivity The energy spectrum of cosmic rays Polarization Faraday rotation: the Galactic magnetic field Loops and spurs The Local Bubble Other galaxies The interstellar medium Temperature states of the ISM 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 Surface brightness The Sun The planets Circumstellar envelopes Circumstellar masers The silicon oxide masers The water masers

5 viii Contents 11.8 The hydroxyl masers Classical novae Non-thermal radiation from binaries and flare stars Recurrent novae X-ray binaries: Cyg X-3 and SS Superluminal motion Pulsars Neutron stars Neutron star structure Rotational slowdown Rotational behaviour of the Crab and Vela pulsars Superfluid rotation Radio and optical emission from pulsars The radiation mechanism The population and evolution of pulsars Searches and surveys; the constraints Trigonometric distance and proper motion X-ray pulsars Magnetic dipole moments Binary orbits and interactions Tests of general relativity Radio galaxies and quasars Radio emission from normal galaxies Spectra and dimensions Structures A simple model of active galactic nuclei The accretion disc The torus The core and the jets Spectra of quasars and other AGNs The radio brightness temperature of the core Superluminal motion The radio j ets and lobes The kiloparsec scale radio sources Cosmology and the cosmic microwave background The Hubble flow A simple Newtonian model Relativistic cosmology 301

6 Contents 14.4 Two fundamental problems of cosmology Big Bang cosmology The cosmic microwave background Anisotropy and distortions of the CMB Cosmology: discrete radio sources and gravitational lenses Evolution and the radio source counts Angular diameter and expansion velocity Gravitational lensing Observations of lenses: rings, quads and others Weak gravitational imaging Time delay The place of radio in astronomy The cosmic microwave background The interstellar medium Angular resolution: stars and quasars Future developments 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