Introduction to Radio Astronomy Jeremy Waller

1. Introduction to Radio AstronomyJeremy Waller Crab Nebula & Pulsar Jodrell Bank Telescope 100” Hooker Telescope

2. Road Map Ptolemy Tycho Brahe S & T Keppler Bayer Galileo Flamsteed Newton Refracting Telescope S & T Argelander Siedel Abbe Schott Gauss Maxwell Hertz Communications WW2 Reflecting Telescope Jansky Antennas Aka: Radio Telescopes Reber Wiener Kolmogoroff Radio Visual Sky Map Satellite Comms. Astronomy Adaptive Optics Pulsars Quasars Radio Galaxies Planets Stars Sun DSP Interferometers VLA Statistical Communications

3. Brief History of Communications • Properties of Electromagnetic Radiation • -What is Electromagnetic Radiation? • -Frequency and Wavelength • -Inverse-Square Law of Propagation • Electromagnetic Spectrum • Causes of Electromagnetic Emissions • -Blackbody Characteristics • -Thermal Radiation • -Continuum Emissions • (eg. Planetry Nebulae, Galactic nuclei, Comets) • -Line Spectra Emission … Atoms and Molecules • -Other sources • Synchrotron Radiation • Representative Sources of RF • -Star • -Pulsar • -Jupiter • The Radio Telescope

4. Sources of RF: • Stars: • -Variable Stars • -Pulsars • -Sun • Galactic and Extragalactic Sources: • -Quasars • Planetary: • -Jupiter System • -Moon • -Comets • Sources of Interference: • -Sun • -Lightning • -Ionosphere • -Power grid, transformers, distribution • - Radars- military and others • -Radio and TV transmitters • -Satellite transmitters • -Mobile phones

5. History of Communications 1800 – 1837 Volta discovers the battery Mathematics – Laplace, Fourier, Cauchy Oersted, Ampere, Faraday, Henry, Ohms Law (1826) Early Telegraph Systems (Gauss & Weber) (Wheatstone & Cooke) 1838 – 1866 Birth of Telegraphy – Transatlantic cable (1866) Pulse Response of a cable calculated(1855) – Lord Kelvin. 1864 A Dynamical Theory of the Electromagnetic Field” J.C.Maxwell – Predicts EM Radiation 1876 – 1899 The Birth of Telephony Stowger devises the step by step switch. 1887-1907 Hertz verifies Maxwells theory 1904-1920 Electronics Applied to Radio and Telephone 1920-1928 Papers by Nyquist, Carson, Hartley

6. History of Communications – cont. 1923-1938 Birth of Television 1939-1945 – WW2 Radar and Microwave Systems developed Wiener and Kolmogoroff – Statistical Signal Detection 1948 A Mathematical Theory of Communication Claude Shannon. . . .

7. EM wave Propagates as a series Of Electric and Magnetic fields Time (t) E field E cw ccw H H field Time (t) “ Front View ” • Polarisation – Direction of E field Vector • Linear • -Vertical, Horizontal or other angle • Elliptical • - Circular • -RH or LH Field variation with time Notice: Electric field is closed - does not terminate on a charge.

8. Property of the Radiated Energy 3 m 9 2 m 4 1 m 1 Isotropic Radiator • Inverse Square Law • -Power per unit area • falls as the square of • the distance from the • source • Doubling the distance • reduces the power per • square metre by x4

9. Effects on RF Emissions • Earths Atmosphere • -Atmospheric “Windows” • -Absorption and Emission Lines • -Reflection • -Refraction • -Phase • -Scintillation • -Faraday Rotation • Source Motion & Gravity • -Doppler Effect • -Gravitational Red Shifting • -Gravitational Lensing • -Occultations

10. Atmospheric Absorption Spacecraft 100% Absorption Radio Telescopes 0% 4.54 mm … 66GHz.

11. Karl Jansky (engineer) • Bell Telephone Laboratories • - 1931` • - Identifying sources of interference • with radio telephone service. • - Rotatable Antenna tuned to 20.5 MHz • -Diameter … 100 ft (30 m). • -Height … 20 ft (6 m) • Three types of static: • -Nearby thunderstorms • -Distant thunderstorms, • -Faint hiss of unknown origin. • - Period  23 hours : 56 minutes. • Comparing the above observations with optical astronomical maps • Conclusion: • -The radiation (Hiss) was coming from the Milky Way • -Peaked in the direction of the centre of the galaxy, • in the constellation of Sagittarius.

12. Grote Reber • -Pioneer of Radio Astronomy • -9 m Paraboloidal antenna (1937) … Radio Telescope • -Repeats Jansky’s work • -Conducts the first sky survey in the radio frequencies.

13. Pulsars as an example Jocelyn Bell Discovers the Pulsar in 1967 • RadioTelescope: • -2000 dipoles • -4.5 acres and • -Operational in July 1967 • -Aperture Synthesis

14. Strong Radio Sources: (Radiance … Jansky) 10 MHz 100 MHz 1 GHz 10 GHz Cassiopeia A 100000 19500 3300 1000 Supernova remnant Cygnus A 70000 13800 2340 300 Radio galaxy Sagittarius A 4000 2000 Center of our galaxy Centaurus A 3000 2000 Peculiar galaxy Virgo A 10000 1800 250 100 M87, galaxy with "jet" Taurus A 1700 955 M1 - Crab Nebula - SN remnant Sun, quiet100 10 000 100 000 1E+6 Sun, disturbed 1E+7 1E+8 1E+8 1E+8 Moon0.1 3 50 10000 Jupiter 1E+7 0 0 50 Sky background 2E+7 3E+6 1E+6 3E+5 Source: "Radio Astronomy" by Kraus, McGraw-Hill 1966

15. Milky Way in Various Wavelengths: Infra-Red Radio X-Ray Visible From Griffith Observatory and JPL),

16. Radio View of the Milky Way

17. Radio continuum emission Example • (Staff Research at AAT) • Gamma Velorum • - Nearest and brightest Wolf Rayet star • -Binary system with an O-star • companion and an orbital period of 79 days. • -Radio Continuum RF @ 10 GHz (3 cm) • -30 mJansky • Observation • RF is non-thermal in origin and • arises from shock fronts which form as the stellar wind from the Wolf Rayet star collides with the stellar wind of the O-star. • Monitoring continuum RF at 3, 6, 13 and 20 cm over a three-month period. Initial results indicate that radio variability is indeed present.

18. Pulsar as an example • Tutorial on Pulsars – Jodrell Bank • http://www.jb.man.ac.uk/~pulsar/Education/Tutorial/tut/tut.htm •   -Duty cycle ~ 5%  -Some Individual pulses very variable in intensity  -Stable profile if several hundred pulses added  -Strongly linearly polarised  -Monotonic polarisation position angle swing through • the pulse implies the origin is near a magnetic pole •  -Very high brightness temperature implies coherent emission  -Drifting subpulses  -Mode changing

19. The lighthouse model of a radio pulsar: A rapidly central neutron star with a strong magnetic field, inclined to the rotation axis with radio emission emanating from the magnetic poles The lighthouse model of a radio pulsar: Wobble in the spin axis

20. Radio Emissions From Jupiter Bernard Burke and Kenneth Franklin of the Carnegie Institution in Washington D.C. discovered that the planet Jupiter was a strong source of radio waves. One arm of Mills Cross Array (circa 1954)

21. Radio Emissions From Jupiter • Synchrotron radiation between 70MHz to over 20 GHz • - At < 40 MHz the planet’s radio emission • is dominated by emissions many orders stronger • than the synchrotron radiation. • 1E+7 J @ 10 MHz. • Known causes • Planetary rotation modulation, • Modulation by Io and/or its torus, • Influence by the solar wind. • Significant number of radio variations • are not currently explained by any known mechanism.

23. Prime Focus Feed Casagrain Feed Secondary Reflector • The Radio Telescope: • -Antenna • -Single Antenna • -Array Antenna • -Receiver • -Low Noise front end • -Signal Processing • -Depends on what • one wants done !! Paraboloidal Reflector Antenna Array

24. The Radio Telescope • Will be quite Large • Need extremely high Resolution at the longer wavelengths • Looking for very weak signals • -Very distant sources • Emissions may be weak (eg. Gamma Velorum) • -eg Continuum emissions Receiver Channel #1 ADC IF Amp Frequency Translation Low Noise Amp Antenna Control R 21 Antenna & Receiver Array R 11 R 22 • Signal Processing System • -Experiment (?) • -Beam Forming • -Aperture synthesis • -Signal Enhancement and Detection • -Signal Properties • -Signal Strength (t) • -RF Doppler • -Polarisation • -Image forming R 01 R 12 R 23 R 02 R 13 R 03

25. THE END • Any Questions ? • SETI • Discussions at the Maid and Magpie • Date? … TBD