X‐HESS: A large sample of highly accreting serendipitous AGN under the XMM‐Newton microscope

Abstract

The bulk of X-ray spectroscopic studies of active galactic nuclei (AGN) are focused on local (z < 0.1) sources with low-to-moderate (<0.3) Eddington ratio (𝜆 Edd ). It is then mandatory to overcome this limitation and improve our understanding of highly accreting AGN. In this work, we present the preliminary results from the analysis of a sample of ∼ 70 high-𝜆 Edd radio-quiet AGN at 0.06 ≤ z ≤ 3.3, based on the 10th release of the XMM-Newton serendipitous source catalog, that we named as XMM-Newton High-Eddington Serendipitous AGN Sample (X-HESS). Almost ∼ 35% of the X-HESS AGN have multi-epoch archival observations and ∼ 70% of the sources can rely on simultaneous OM optical data. First results reveal sources showing signatures of ultra-fast outflows and remarkable long-and short-term X-ray flux variations. Indeed in SDSS J095847.88+690532.7 (z ∼ 1.3), one of the most densely monitored objects hosting a ∼ 10 9 M ⊙ supermassive black hole, we discovered a variation of the soft X-ray flux by a factor of >2 over approximately one week (rest-frame). Large variations in the power-law continuum photon index Γ are also observed, questioning expectations from previously reported Γ − 𝜆 Edd relations, for which Γ ≥ 2 would be a ubiquitous hallmark of AGN with 𝜆 Edd ∼ 1.