Obscuring clouds playing hide-and-seek in the active nucleus H0557-385

Abstract

This Letter reports on two XMM-Newton observations of the type 1 Seyfert 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 Kα line associated with a Compton reflection continuum. An additional spectral line around 6.6 keV is required to fit Kα emission from Fe XXV. The spectral curvature below 6 keV implies obscuration by neutral gas with a column density of ~8 × 1023 cm -2 partially covering the primary emission, which still contributes a few per cent of the soft X-ray emission. Absorption by ionized 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. © 2009 The Authors. Journal compilation © 2009 RAS.