The Cocoon Shocks of Cygnus A: Pressures and Their Implications for the Jets and Lobes

Snios, Bradford; Nulsen, Paul E. J.; Wise, Michael W.; de Vries, Martijn; Birkinshaw, Mark; Worrall, Diana M.; Duffy, Ryan T.; Kraft, Ralph P.; McNamara, Brian R.; Carilli, Chris; Croston, Judith H.; Edge, Alastair C.; Godfrey, Leith E. H.; Hardcastle, Martin J.; Harris, Daniel E.; Laing, Robert A.; Mathews, William G.; McKean, John P.; Perley, Richard A.; Rafferty, David A. and Young, Andrew J. (2018). The Cocoon Shocks of Cygnus A: Pressures and Their Implications for the Jets and Lobes. The Astrophysical Journal, 855(1), article no. 71.

DOI: https://doi.org/10.3847/1538-4357/aaaf1a

Abstract

We use 2.0 Msec of Chandra observations to investigate the cocoon shocks of Cygnus A and some implications for its lobes and jet. Measured shock Mach numbers vary in the range 1.18-1.66 around the cocoon. We estimate a total outburst energy of ≃4.7×10⁶⁰ erg, with an age of ≃2×10⁷ years. The average postshock pressure is found to be 8.6±0.3×10⁻¹⁰ erg cm⁻³, which agrees with the average pressure of the thin rim of compressed gas between the radio lobes and shocks, as determined from X-ray spectra. However, average rim pressures are found to be lower in the western lobe than in the eastern lobe by ≃20%. Pressure estimates for hotspots A and D from synchrotron self-Compton models imply that each jet exerts a ram pressure ≳ 3 times its static pressure, consistent with the positions of the hotspots moving about on the cocoon shock over time. A steady, one-dimensional flow model is used to estimate jet properties, finding mildly relativistic flow speeds within the allowed parameter range. Models in which the jet carries a negligible flux of rest mass are consistent with with the observed properties of the jets and hotspots. This favors the jets being light, implying that the kinetic power and momentum flux are carried primarily by the internal energy of the jet plasma rather than by its rest mass.

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About

• Item ORO ID
• 53766
• Item Type
• Journal Item
• ISSN
• 1538-4357
• Project Funding Details

• Funded Project Name	Project ID	Funding Body
  Jet energy injection in galaxy groups and clusters - transfer of CG funding (Transfer in)	ST/R00109X/1	STFC (Science & Technology Facilities Council)

• Keywords
• galaxies: active; galaxies: clusters: general; galaxies: individual (Cygnus A) ; X-rays: galaxies
• Academic Unit or School
• Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
  Faculty of Science, Technology, Engineering and Mathematics (STEM)
• Research Group
• Astronomy
• Copyright Holders
• © 2018 The American Astronomical Society
• Depositing User
• Judith Croston