Electron Energy Distribution in Hotspots of Cygnus A:Filling the Gap with Spitzer Space Telescope

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Here we present Spitzer Space Telescope imaging of Cyg A with the Infrared Array Camera at 4.5 {micro}m and 8.0 {micro}m, resulting in the detection of the high-energy tails or cut-offs in the synchrotron spectra for all four hotspots of this archetype radio galaxy. When combined with the other data collected (and re-analyzed) from the literature, our observations allow for detailed modeling of the broad-band (radio-to-X-ray) emission for the brightest spots A and D. We confirm that the X-ray flux detected previously from these features is consistent with the synchrotron self-Compton radiation for the magnetic field intensity B {approx} 170 ... continued below

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28 pages

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Stawarz, L.; Cheung, C.C.; Harris, D.E. & Ostrowski, M. March 6, 2007.

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Here we present Spitzer Space Telescope imaging of Cyg A with the Infrared Array Camera at 4.5 {micro}m and 8.0 {micro}m, resulting in the detection of the high-energy tails or cut-offs in the synchrotron spectra for all four hotspots of this archetype radio galaxy. When combined with the other data collected (and re-analyzed) from the literature, our observations allow for detailed modeling of the broad-band (radio-to-X-ray) emission for the brightest spots A and D. We confirm that the X-ray flux detected previously from these features is consistent with the synchrotron self-Compton radiation for the magnetic field intensity B {approx} 170 {micro}G in spot A, and B {approx} 270 {micro}G in spot D. We also find that the energy density of the emitting electrons is most likely larger by a factor of a few than the energy density of the hotspots magnetic field. We construct energy spectra of the radiating ultrarelativistic electrons. We find that for both hotspots A and D these spectra are consistent with a broken power-law extending from at least 100MeV up to {approx} 100GeV, and that the spectral break corresponds almost exactly to the proton rest energy of {approx} 1GeV. We argue that the shape of the electron continuum most likely reflects two different regimes of the electron acceleration process taking place at mildly relativistic shocks, rather than resulting from radiative cooling and/or absorption e.ects. In this picture the protons inertia defines the critical energy for the hotspot electrons above which Fermi-type acceleration processes may play a major role, but below which the operating acceleration mechanism has to be of a different type. At energies {approx}> 100 GeV, the electron spectra cut-off/steepen again, most likely as a result of spectral aging due to radiative loss effects. We discuss several implications of the presented analysis for the physics of extragalactic jets.

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28 pages

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  • Journal Name: Astrophysical Journal

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  • Report No.: SLAC-PUB-12311
  • Grant Number: AC02-76SF00515
  • DOI: 10.1086/517966 | External Link
  • Office of Scientific & Technical Information Report Number: 900601
  • Archival Resource Key: ark:/67531/metadc883532

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • March 6, 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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Stawarz, L.; Cheung, C.C.; Harris, D.E. & Ostrowski, M. Electron Energy Distribution in Hotspots of Cygnus A:Filling the Gap with Spitzer Space Telescope, article, March 6, 2007; [Menlo Park, California]. (digital.library.unt.edu/ark:/67531/metadc883532/: accessed January 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.