$\text{Herschel}$ discovery of far-infrared emission from the hot spot D in the radio galaxy Cygnus A

Abstract

The far infrared counterpart of hot spot D, the terminal hot spot of the eastern jet hosted by the radio galaxy Cygnus A, is detected with \textit{Herschel} Aperture photometery of the source performed in 5 photometric bands covering the wavelength range of $70\unicode{x2013}350$ $\mu \mathrm{m}$. After removing the contamination from another nearby hot spot, E, the far-infrared intensity of hot spot D is derived as $83\pm 13$ and $269\pm 66$ mJy at $160$ and $350$ $\mu \mathrm{m}$, respectively. Since the far-infrared spectrum of the object smoothly connects to the radio one, the far-infrared emission is attributed to the synchrotron radiation from the radio-emitting electron population. The radio-to-near-infrared spectrum is confirmed to exhibit a far-infrared break feature at the frequency of ${\nu }_{\mathrm{br}}=2.0_{-0.8}^{+1.2}\times 10^{12}$ Hz. The change in energy index at the break ($\Delta \alpha =0.5$) is interpreted as the impact of radiative cooling on an electron distribution sustained by continuous injection from diffusive shock acceleration. By ascribing the derived break to this cooling break, the magnetic field, $B$, in the hot spot is determined as a function of its radius, $R$ within a uniform one-zone model combined with the strong relativistic shock condition. An independent $B$-$R$ constraint is obtained by assuming the X-ray spectrum is wholly due to synchrotron-self-Compton emission. By combining these conditions, the two parameters are tightly determined as $B=120\unicode{x2013}150$ $\mu \mathrm{G}$ and $R=1.3\unicode{x2013}1.6$ kpc. A further investigation into the two conditions indicates the observed X-ray flux is highly dominated by the synchrotron-self-Compton emission.

arXiv comment12 pages, 8 figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Society

References in corpus (40)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• The Astrophysics of Ultrahigh Energy Cosmic Rays
• In-flight calibration of the Herschel-SPIRE instrument
• X-ray Emission Properties of Large Scale Jets, Hotspots and Lobes in Active Galactic Nuclei
• Turbulence and Magnetic Field Amplification in Supernova Remnants: Interactions Between A Strong Shock Wave and Multi-Phase Interstellar Medium
• The origins of X-ray emission from the hotspots of FRII radio sources
• Chandra X-ray Observations of Pictor A: High Energy Cosmic Rays in a Radio Galaxy?
• Magnetic field strengths in the hotspots and lobes of three powerful FRII radio sources
• A Chandra X-ray Study of Cygnus A - III. The Cluster of Galaxies
• Chandra Observations of Cygnus A: Magnetic Field Strengths in the Hot Spots of a Radio Galaxy
• Particle acceleration and relativistic shocks
• AGN Jet Kinetic Power and the Energy Budget of Radio Galaxy Lobes
• Particle content, radio-galaxy morphology and jet power: all radio-loud AGN are not equal
• Variability Pattern and the Spectral Evolution of the BL Lacertae Object PKS 2155-304
• Bayesian methods of astronomical source extraction
• The Cavity of Cygnus A
• Chandra X-Ray Detection of the Radio Hotspots of 3C295
• The Cluster of Galaxies Surrounding Cygnus A
• The Electron Energy Distribution in the Hotspots of Cygnus A: Filling the Gap with the Spitzer Space Telescope
• A Chandra study of particle acceleration in the multiple hotspots of nearby radio galaxies
• LOFAR imaging of Cygnus A -- Direct detection of a turnover in the hotspot radio spectra
• Constraints on the energetics and plasma composition of relativistic jets in FR II sources
• The Cocoon Shocks of Cygnus A: Pressures and Their Implications for the Jets and Lobes
• In-Situ Particle Acceleration in Extragalactic Radio Hot Spots: Observations Meet Expectations
• The estimate of kinetic powers of jets in FRII radio galaxies: existence of invisible components?
• A Radio through X-ray Study of the Hot Spots, Active Nucleus, and Environment of the Nearby FR II Radio Galaxy 3C 33
• Estimate of the total kinetic power and age of extragalactic jet by its cocoon dynamics: The case of Cygnus A
• Cygnus A: A Long Wavelength Resolution of the Hot Spots
• Spitzer Observations of Hotspots in Radio Lobes
• Chandra Observations of the Radio Galaxy 3C 445 and the Hotspot X-ray Emission Mechanism
• Evidence of non-thermal X-ray emission from radio lobes of Cygnus A
• Calorimetry of Active Galactic Nucleus jets: testing plasma composition in Cygnus A
• Discovery of Optical Emission in the Hotspots of Three 3CR Quasars: High-Energy Particle Acceleration in Powerful Radio Hotspots
• Evidence for a significant mixture of electron/positron pairs in FRII jets constrained by cocoon dynamics
• Examining High Energy Radiation Mechanisms of Knots and Hotspots in Active Galactic Nucleus Jets
• On the significance of relativistically hot pairs in the jets of FR II radio galaxies
• Herschel SPIRE discovery of far-infrared excess synchrotron emission from the west hot spot of the radio galaxy Pictor A
• Multiwavelength study of Cygnus A IV. Proper motion and location of the nucleus

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