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Relativistic O VIII Emission and Ionized Outflow in NGC 4051

We present XMM-Newton RGS observations of the soft X-ray spectrum of NGC 4051, and explore their implications for the inner accretion disk and ionized outflow in the active galactic nucleus. We fit the soft X-ray excess with a relativistically broadened O VIII recombination spectrum, including the entire line series and recombination continuum. This plus an underlying power law continuum provides a much better fit to the soft X-ray spectrum than a single temperature or disk blackbody plus power law. The emission line profiles, computed for a Kerr metric around a maximally rotating black hole, reveal a sharply peaked disk emissivity law and inner radius smaller than 1.7 R_G. The spectrum also includes narrow absorption and emission lines from C, N, O, Ne, and Fe in an ionized outflow. Outflow column densities are relatively low and do not create significant edges in the spectrum. The small amount of absorption bolsters confidence in the detection of relativistic emission line features. The narrow-line emitter has a large (76%) global covering fraction, leading to strong forbidden lines and filling in of the resonance absorption lines. We also find broad C VI Ly-alpha and very broad O VII emission from the broad-line region. The narrow and broad-line regions span large ranges in ionization parameter, and may arise in a disk outflow. The ionized absorber has a large ionization range which is inconsistent with pressure equilibrium in a multiphase medium. The mass outflow rate exceeds the accretion rate by a factor of one thousand.