XMM-Newton observations of bright ROSAT selected active galactic nuclei with low intrinsic absorption

Abstract

We present a sample of twenty-one ROSAT bright active galactic nuclei (AGN), representing a range of spectral classes, and selected for follow-up snap-shot observations with XMM-Newton. The typical exposure was between 5-10 ks. The objects were primarily selected on the bases of X-ray brightness and not on hardness ratio; thus the sample cannot be strictly defined as a `soft' sample. One of the main outcomes from the XMM-Newton observations was that all of the AGN, including eleven type 1.8-2 objects, required low levels of intrinsic absorption (nh < 10^21 cm^-2). The low absorption in type 2 systems is a challenge to account for in the standard orientation-based unification model, and we discuss possible physical and geometrical models which could elucidate the problem. Moreover, there does not appear to be any relation between the strength and shape of the soft excess, and the spectral classification of the AGN in this sample. We further identify a number of AGN which deserve deeper observations or further analysis: for example, the LINERs NGC 5005 and NGC 7331, where optically thin thermal and extended emission is detected, and the narrow-line Seyfert 1 II Zw 177, which shows a broad emission feature at 5.8keV.