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

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 N_H 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.