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 $>70$ keV. In gross terms, the NuSTAR spectrum of the AGN has the form of a power law ($\Gamma \sim 1.6-1.7$) absorbed by a neutral column density of $N_H\sim 1.6\times {10}^{23}{cm}^{-2}$. However, we also detect curvature in the hard ($>10$ 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 $E_{cut}>111$ keV(90% confidence). Interestingly, the absorbed power law plus reflection model leaves residuals suggesting the absorption/emission from a fast ($15,000-26,000km{s}^{-1}$), high column-density ($N_W>3\times {10}^{23}{cm}^{-2}$), highly ionized ($\xi \sim 2500ergcm{s}^{-1}$) 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.