High-resolution X-ray and Ultraviolet Spectroscopy of the Complex Intrinsic Absorption in Ngc 4051 with Chandra and Hst

We present the results from simultaneous observations of the Narrow-Line Seyfert 1 galaxy NGC 4051 with the Chandra High Energy Transmission Grating Spectrometer and the HST Space Telescope Imaging Spectrograph. The X-ray grating spectrum reveals absorption and emission lines from hydrogen-like and helium-like ions of O, Ne, Mg and Si. We resolve two distinct X-ray absorption systems: a high-velocity blueshifted system at −2340± 130 km s−1 and a low-velocity blueshifted system at −600± 130 km s−1. In the UV spectrum we detect strong absorption, mainly from C IV, N V and Si IV, that is resolved into as many as nine different intrinsic absorption systems with velocities between −650 km s−1 and 30 km s−1. Although the low-velocity X-ray absorption is consistent in velocity with many of the UV absorption systems, the high-velocity X-ray absorption seems to have no UV counterpart. In addition to the absorption and emission lines, we also observe rapid X-ray variability and a state of low X-ray flux during the last ≈ 15 ks of the observation. NGC 4051 has a soft X-ray excess which we fit in both the high and low X-ray flux states. The high-resolution X-ray spectrum directly reveals that the soft excess is not composed of narrow emission lines and that it has significant spectral curvature. A power-law model fails to fit it, while a blackbody produces a nearly acceptable fit. We compare the observed spectral variability with the results of previous studies of NGC 4051. Subject headings: galaxies: active — galaxies: nuclei — galaxies: individual (NGC 4051) — galaxies: Seyfert — X-rays: galaxies — ultraviolet: galaxies