Obscuring clouds playing hide-and-seek in the Active Nucleus H0557-385

TL;DR

This study analyzes two XMM-Newton observations of Seyfert 1 galaxy H0557-385, revealing that flux variations are caused by intervening high-density clouds obscuring the nucleus, with spectral features indicating complex absorption and reflection.

Contribution

It provides detailed spectral analysis showing that flux changes are due to line-of-sight clouds, and characterizes the obscuring material's properties in H0557-385.

Findings

Flux variation caused by high-density clouds obscuring the nucleus.

Detection of neutral and ionized absorption features in the spectrum.

Presence of strong Fe Kalpha line and Compton reflection continuum.

Abstract

This paper reports on two XMM-Newton observations of the Seyfert 1 Galaxy H0557-385 obtained in 2006, which show the source at an historical low flux state, more than a factor of 10 lower than a previous XMM-Newton look in 2002. The low flux spectrum presents a strong Fe Kalpha line associated to a Compton reflection continuum. An additional spectral line around 6.6 keV is required to fit Kalpha emission from Fe XXV. The spectral curvature below 6 keV implies obscuration by neutral gas with a column density of 8*10^{23}cm^{-2} partially covering the primary emission, which still contributes for a few percent of the soft X-ray emission. Absorption by ionised material on the line of sight is required to fit the deep trough below 1 keV. The comparison of the two spectral states shows that the flux transition is to be ascribed entirely to intervening line-of-sight clouds with high column density.