Past exam of the symmetry and relativity course of the University of Oxford / 2015 / 1 / c / ii / Solution 2026-10-25
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Relativistic relativistic aberration concentrates emission into an angular scale
(1)
This is a half-angle or characteristic divergence scale; a full cone opening is about twice it. The exact half-photon-count cone in a applies to isotropic rest-frame emission. A synchrotron emitter has its own rest-frame angular radiation pattern, so that count result should not be treated as an exact median-power formula for the synchrotron beam. It nevertheless gives the correct relativistic beaming scale. Electron-beam emittance, vertical angular spread and the detector's acceptance can broaden the experimentally observed divergence beyond this intrinsic estimate.
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