The X-ray/UV absorber in NGC 4593

Abstract

We present the results of a recent (2011 March) 160 ks Chandra-LETGS (Low Energy Transmission Grating Spectrometre) observation of the Seyfert galaxy NGC 4593, and the analysis of archival X-ray and UV spectra taken with XMM-Newton and Hubble Space Telescope (HST)/STIS (Space Telescope Imaging Spectrograph) in 2002. We find evidence of a multi-component warm absorber (WA) in the X-rays with four distinct ionization degrees (log ξ = 1.0, log ξ = 1.7, log ξ = 2.4 and log ξ = 3.0) outflowing at several hundreds of km s^-1. In the UV we detect 15 kinematic components in the absorbers, blueshifted with respect to the systemic velocity of the source, ranging from -60 km s^-1 to -1520 km s^-1. Although the predicted C IV and N V column densities from the low-ionization X-ray outflow are in agreement with those measured for some components in the STIS spectrum, there are kinematic discrepancies that may prevent both the X-ray and UV absorbers from originating in the same intervening gas. We derive upper limits on the location of the absorbers finding that the high-ionization gas lies within ∼6-29 pc from the central ionizing source, while the low-ionization gas is located at several hundreds of pc. This is consistent with our line of sight passing through different parts of a stratified wind. The total kinetic energy of the outflows injected into the surroundings of the host galaxy only accounts for a tiny fraction of the bolometric luminosity of the source and it is therefore unlikely that they may cause a significant impact on the interstellar medium of NGC 4593 in a given single episode of activity.