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

Abstract

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 themore » 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.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
900601
Report Number(s):
SLAC-PUB-12311
Journal ID: ISSN 0004-637X; ASJOAB; astro-ph/0701568; TRN: US0702345
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ABSORPTION; ACCELERATION; AGING; CAMERAS; DETECTION; ELECTRON SPECTRA; ELECTRONS; ENERGY DENSITY; ENERGY SPECTRA; MAGNETIC FIELDS; PHYSICS; PROTONS; RADIATIONS; RADIATIVE COOLING; SPECTRA; SYNCHROTRONS; TELESCOPES; Astrophysics,ASTRO

Citation Formats

Stawarz, L., Cheung, C.C., Harris, D.E., and Ostrowski, M. Electron Energy Distribution in Hotspots of Cygnus A:Filling the Gap with Spitzer Space Telescope. United States: N. p., 2007. Web. doi:10.1086/517966.
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. United States. doi:10.1086/517966.
Stawarz, L., Cheung, C.C., Harris, D.E., and Ostrowski, M. Tue . "Electron Energy Distribution in Hotspots of Cygnus A:Filling the Gap with Spitzer Space Telescope". United States. doi:10.1086/517966. https://www.osti.gov/servlets/purl/900601.
@article{osti_900601,
title = {Electron Energy Distribution in Hotspots of Cygnus A:Filling the Gap with Spitzer Space Telescope},
author = {Stawarz, L. and Cheung, C.C. and Harris, D.E. and Ostrowski, M.},
abstractNote = {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.},
doi = {10.1086/517966},
journal = {Astrophysical Journal},
number = ,
volume = ,
place = {United States},
year = {Tue Mar 06 00:00:00 EST 2007},
month = {Tue Mar 06 00:00:00 EST 2007}
}