Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots

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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 {approx} 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 ... continued below

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5 pages

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Cheung, C.C.Teddy; Stawarz, L.; Harris, D.E. & Ostrowski, M. October 15, 2007.

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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 {approx} 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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5 pages

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  • Invited talk at International Meeting on Extragalactic Jets: Theory and Observation from Radio to Gamma Ray, Girdwood, Alaska, 21-24 May 2007

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  • Report No.: SLAC-PUB-12863
  • Grant Number: AC02-76SF00515
  • Office of Scientific & Technical Information Report Number: 918018
  • Archival Resource Key: ark:/67531/metadc885390

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  • October 15, 2007

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  • Sept. 22, 2016, 2:13 a.m.

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  • Dec. 5, 2016, 2:49 p.m.

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Cheung, C.C.Teddy; Stawarz, L.; Harris, D.E. & Ostrowski, M. Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots, article, October 15, 2007; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc885390/: accessed September 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.