Detectability of low-energy X-ray spectral components in type 1 active galactic nuclei

Abstract

In this paper we examine the percentage of type 1 active galactic nuclei (AGN) which require the inclusion of a soft excess component and/or significant cold absorption in the modelling of their X-ray spectra obtained by XMM?Newton . We do this by simulating spectra which mimic typical spectral shapes in order to find the maximum detectability expected at different count levels. We then apply a correction to the observed percentages found for the Scott et al. sample of 761 sources. We estimate the true percentage of AGN with a soft excess component to be 75 ± 23 per cent, suggesting that soft excesses are ubiquitous in the X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count spectra in narrow z bins in which additional spectral components were not originally detected, we show that the soft excess feature is recovered with a mean temperature kT and blackbody-to-power-law normalization ratio consistent with those of components detected in individual high count spectra. Cold absorption with NH values broadly consistent with those reported in individual spectra is also recovered. We suggest such intrinsic cold absorption is found in a minimum of ?5 per cent of type 1 AGN and may be present in up to ?10 per cent.