NuSTAR Observations of the Powerful Radio Galaxy Cygnus A

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 components. NuSTAR gives a source-dominated spectrum of the AGN out to \gt 70 keV. 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 {N}_{{H}}∼ 1.6× {10}²³ {{cm}}^-2. However, we also detect curvature in the hard (\gt 10 keV) 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 {E}_{cut}\gt 111 keV(90% confidence). Interestingly, the absorbed power law plus reflection model leaves residuals suggesting the absorption/emission from a fast (15,000-26,000 {km} {{{s}}}^-1 ), high column-density ({N}_W\gt 3× {10}²³ {{cm}}^-2), highly ionized (ξ ∼ 2500 {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.