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Exploring Coronal Faraday Rotation in Radio Astronomy

Explore the definition, measurement techniques, and future potential of Coronal Faraday Rotation in radio astronomy using various radio sources and spacecraft data. Discover the impact of solar phenomena on Faraday Rotation variations over different time scales.

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Exploring Coronal Faraday Rotation in Radio Astronomy

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  1. Coronal Faraday Rotation of Occulted Radio Signals M. K. Bird Argelander-Institut für Astronomie, Universität Bonn International Colloquium on Scattering and Scintillation in Radio Astronomy Pushchino, Russia Monday, 19 June 2006

  2. Coronal Faraday Rotation – Definition Coronal FR using Various Radio Sources Pulsars Extended Continuum Sources Spacecraft (Helios E12: 1975-1984) FR Variations over Different Time Scales Background Coronal Magnetic Field FR Signature of Coronal Mass Ejections FR Fluctuations: Alfvén Waves & Quasi-harmonic Oscillations Coronal FR Mapping – the Future? Summary Outline

  3. Coronal Faraday Rotation - Definition

  4. Faraday Rotation : Definition radians with 2.36∙104 in MKS or cgs units radio frequency (Helios: 2.3 GHz) electron density mag field proj. along ray path

  5. Interplanetary Electron Column Density from Earth I = ∫Ne(s) ds “Dispersion Measure” Units: hexems 1 hexem = 1016 el/m2 Earth Sun analogous plot for Faraday Rotation does not exist!

  6. Polarization Angle Measurement Electric Vectors (semi-major axis of polarization ellipse): E0 = Source (transmitted) E= Measured (received) Angle definitions: q = locally measured polarization angle p = parallactic angle  = Faraday rotation

  7. Rotation Measure RM: A rotation measure of RM = 1 rad m-2 yields: • = 0.97° at 2.3 GHz (=0.13 m) • = 57.3° at 300 MHz (=1.0 m) • = 1432° at 60 MHz (=5.0 m)

  8.  can be positive or negative (from polarity of interplanetary magnetic field) Angle ambiguity (   ± m·180°) Contributions from electron density and magnetic field cannot be separated without independent measurements Correction for variable ionosphere necessary if solar offset R > 10 RS Coronal Faraday Rotation Measurement

  9. Ionospheric Faraday Rotation

  10. Coronal FR using Various Radio Sources

  11. Coronal FR with Pulsars

  12. Pulsars at Conjunction 1978-79 [Bird et al., Nature 283, 459-460, 1980]

  13. Pulsar Pulse Profiles: Measurement Technique intrinsic profile modified profile p-angle: intrinsic & modified PSR 0540+23 PSR 0525+21

  14. Coronal FR of PSR 0525+21 (1978-79)

  15. Solwind Images during 1979 Occultation of PSR 0525+21

  16. Coronal Magnetic Field from RM & DM: 1979

  17. Coronal FR with Extended ContinuumSources 3C228 A [Spangler, 2005] 1' B C

  18. Coronal FR at VLA: 21 Aug 2003 3C228 R = 7.1…6.2 RS RM: 62.5 rad/m2

  19. SOHO/LASCO: 16 AUG 2003 3C228 3C228 Venus Jupiter

  20. Coronal FR with Helios • Helios – 1 • Launch: 10 Dec 1974 • EOM: 15 Mar 1986 • q = 0.31 AU (P = 190 d) • i = 0°, "spin up" • Helios – 2 • Launch: 15 Jan 1976 • EOM: 08 Jan 1981 • q = 0.29 AU (P = 186 d) • i = 0°, "spin down"

  21. Earth-Sun Line Fixed: Helios-1

  22. Coronal Faraday Rotation: Helios Observations <FR> = 35.4° FR = 2.1°

  23. Helios FR: Effelsberg/Goldstone

  24. Coronal FR: Helios-1, Dec 1981 180 ambiguity

  25. FR Variations over Different Time Scales …Background Coronal Magnetic Field

  26. Ballerina Model of HCS

  27. Radio Ray Path Geometry in the Corona

  28. Coronal Faraday Rotation from Sector Structure

  29. Mean Absolute FR: 1975-1976 |max| R-4.15

  30. Coronal Electron Density: Radial Profiles

  31. Mean Coronal Magnetic Field 1975-76 [Pätzold et al., Solar Phys. 109, 91, 1987] 3 RS < R < 10 RS: Br = 7.9 R-2.7 G (17) or Br = 6 R-3 + 1.2 R-2 G (18)

  32. FR Variations over Different Time Scales … FR Fluctuations: Alfvén Waves & Quasi-harmonic Oscillations

  33. FR Fluctuations: Standard Deviation vs. Solar Offset

  34. FR Spectra for Various Solar Offset Distances Andreev et al., [1996]

  35. FR Spectral Index vs Solar Offset

  36. Two-Station Coronal Sounding Measurements

  37. Measuring Coronal Velocities

  38. Coronal Velocities from FR Correlations

  39. Two-Station FR Measurements

  40. Simultaneous FR Spectra with QHC

  41. Rapid Sequence of FR Spectra QHC comes… … and goes! [Chashei et al., 1999]

  42. FR Variations over Different Time Scales … FR Signature of Coronal Mass Ejections

  43. CME Passing through Helios-2 Ray Path Solwind Coronagraph Images recorded during Helios Solar Occultations In Oct/Nov 1979 [Bird et al., 1985]

  44. CME Height-Time Diagram, 24 Oct 1979

  45. CME Magnetic Field Estimates, 24 Oct 1979

  46. Coronal FR Mapping – the Future?

  47. One line of sight to a linearly polarized source

  48. Simulated Coronal FR for CR 1751 [J. Kasper, priv. comm, 2004.]

  49. Transient Simulations: October 2003 CMEs CME! Large FR in  20 sources CME not yet detected

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