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Paper: Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots
Volume: 386, Extragalactic Jets: Theory and Observation from Radio to Gamma Ray
Page: 139
Authors: Cheung, C.C.; Stawarz, L.; Harris, D.E.; Ostrowski, M.
Abstract: We report new detections of the hotspots in Cygnus A at 4.5 and 8.0 microns with the Spitzer Space Telescope. Together with detailed published radio observations and synchrotron self-Compton modeling of previous X-ray detections, we reconstruct the underlying electron energy spectra of the two brightest hotspots (A and D). The low-energy portion of the electron distributions have flat power-law slopes (s ∼ 1.5) up to the break energy which corresponds almost exactly to the mass ratio between protons and electrons; we argue that these features are most likely intrinsic rather than due to absorption effects. Beyond the break, the electron spectra continue to higher energies with very steep slopes s >3. Thus, there is no evidence for the ‘canonical’ s=2 slope expected in 1st order Fermi-type shocks within the whole observable electron energy range. We discuss the significance of these observations and the insight offered into high-energy particle acceleration processes in mildly relativistic shocks
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