Compton–Getting effect

The Compton–Getting effect is an apparent anisotropy in the intensity of radiation or particles due to the relative motion between the observer and the source. This effect was first identified in the intensity of cosmic rays by Arthur Compton and Ivan A. Getting in 1935.[1] Gleeson and Axford provide a full derivation of the equations relevant to this effect.[2]

The original application of the Compton–Getting effect predicted that the intensity of cosmic rays should be higher coming from the direction in which Earth is moving.[2][3] For the case of cosmic rays the Compton–Getting effect only applies to those that are unaffected by the Solar wind such as extremely high energy rays.[2] It has been calculated that the speed of the Earth within the galaxy (200 kilometres per second (120 mi/s))[3] would result in a difference between the strongest and weakest cosmic ray intensities of about 0.1%.[4] [2] This small difference is within the capabilities of modern instruments to detect,[4] and was observed in 1986.[5] Forman (1970) derives the Compton–Getting effect anisotropy from the Lorentz invariance of the phase space distribution function.[6] Ipavich (1974) furthers this general derivation to derive count rates with respect to the flow vector.[7]

This Compton–Getting effect is apparent in plasma data in Earth's magnetotail.[8] The Compton–Getting effect has also been utilized for analyzing energetic neutral atom (ENA) data returned by the Cassini-Huygens spacecraft at Saturn.[9]

Notes
  1. Compton, A. H.; Getting, I. A. (June 1, 1935). "An Apparent Effect of Galactic Rotation on the Intensity of Cosmic Rays". Physical Review. 47 (11): 817–821. Bibcode:1935PhRv...47..817C. doi:10.1103/PhysRev.47.817.
  2. Gleeson, L. J.; Axford, W. I. (December 1968). "The Compton-Getting Effect". Astrophysics and Space Science. 2 (4): 431–437. Bibcode:1968Ap&SS...2..431G. doi:10.1007/BF02175919.
  3. "Pierre Auger Observatory Q&A". 2005. Archived from the original on 2009-02-12. Retrieved 2009-03-21.
  4. Clay, Roger; Dawson, Bruce (1997). Cosmic Bullets. NSW, Australia: Allen & Unwin. p. 103. ISBN 978-1-86448-204-1.
  5. Cutler, D. J.; Groom, D. E. (July 1986). "Observation of terrestrial orbital motion using the cosmic-ray Compton-Getting effect". Nature. 322 (6078): 434–436. Bibcode:1986Natur.322..434C. doi:10.1038/322434a0.
  6. Forman, M. (1970). "The Compton-Getting effect for cosmic-ray particles and photons and the Lorentz invariance of distribution functions". Planet. Space Sci. 18 (1): 25–31. Bibcode:1970P&SS...18...25F. doi:10.1016/0032-0633(70)90064-4.
  7. Ipavich, F. M. (1974). "The Compton-Getting effect for low energy particles". Geophys. Res. Lett. 1 (4): 149–152. Bibcode:1974GeoRL...1..149I. doi:10.1029/GL001i004p00149. hdl:2060/19750006513.
  8. Roelof, E. C.; Keath, E. P.; Bostrom, C. O.; Williams, D. J. (May 1, 1976). "Fluxes of >50-keV Protons and >30-keV Electrons at ~ 35 Re 1. Velocity Anisotropies and Plasma Flow in the Magnetotail". J. Geophys. Res. 81 (13): 2304–2314. Bibcode:1976JGR....81.2304R. doi:10.1029/JA081i013p02304.
  9. Paranicas, C.; D. G. Mitchell; E. C. Roelof; P. C. Brandt; D. J. Williams; S. M. Krimigis; B. H. Mauk (2 November 2005). "Periodic intensity variations in global ENA images of Saturn". Geophys. Res. Lett. 32 (21): L21101. Bibcode:2005GeoRL..3221101P. doi:10.1029/2005GL023656.


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