NuSTAR Observations of the Powerful Radio-Galaxy Cygnus A

Christopher S. Reynolds, Anne M. Lohfink, Patrick M. Ogle, Fiona A. Harrison, Kristin K. Madsen, Andrew C. Fabian, Daniel R. Wik, Grzegorz Madejski, David R. Ballantyne, Steven E. Boggs, Finn Erland Christensen, William W. Craig, Felix Fuerst, Charles J. Hailey, Lauranne Lanz, Jon M. Miller, Cristian Saez, Daniel Stern, Dominic J. Walton, William Zhang

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Abstract

We present NuSTAR observations of the powerful radio galaxy Cygnus A,focusing on the central absorbed active galactic nucleus (AGN). Cygnus A is embedded in a cool-core galaxy cluster, and hence we also examine archival XMM-Newton data to facilitate the decomposition of the spectrum into the AGN and intracluster medium (ICM) components. NuSTAR gives a source-dominated spectrum of the AGN out to >70keV. In gross terms, the NuSTAR spectrum of the AGN has the form of a power law (Γ~1.6-1.7) absorbed by a neutral column density of NH~1.6x1023 cm-2. However, we also detect curvature in the hard (>10keV) spectrum resulting from reflection by Compton-thick matter out of our line-of-sight to the X-ray source. Compton reflection, possibly from the outer accretion disk or obscuring torus, is required even permitting a high-energy cut off in the continuum source; the limit on the cut off energy is Ecut>111keV (90% confidence). Interestingly, the absorbed power-law plus reflection modelleaves residuals suggesting the absorption/emission from a fast(15,000-26,000km/s), high column-density (NW>3x1023 cm-2), highly ionized (ξ~2,500 erg cm/s-1) wind. A second, even faster ionized wind component is also suggested by these data. We show that the ionized wind likely carries a significant mass and momentum flux, and may carry sufficient kinetic energy to exercise feedback on the host galaxy. If confirmed, the simultaneous presence of a strong wind and powerful jets in Cygnus A demonstrates that feedback from radio-jets and sub-relativistic winds are not mutually exclusive phases of AGN activity but can occur simultaneously.
Original languageEnglish
Article number154
JournalAstrophysical Journal
Volume808
Pages (from-to)13
ISSN0004-637X
DOIs
Publication statusPublished - 2015

Keywords

  • Accretion
  • Accretion disks
  • Galaxies: clusters: intracluster medium
  • Galaxies: jets
  • X-rays: individual (Cygnus A)

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