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 ($\hat{I}{»}_{\mathrm{Edd}}$). 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 $\sim 70$ high-$\hat{I}{»}_{\mathrm{Edd}}$ radio-quiet AGN at $0.06\le z\le 3.3$, based on the 10th release of the XMM-Newton serendipitous source catalogue, that we named as XMM-Newton High-Eddington Serendipitous AGN Sample (X-HESS). Almost $\sim 35\%$ of the X-HESS AGN have multi-epoch archival observations and $\sim 70\%$ 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 J095847.88+690532.7 ($z\sim 1.3$), one of the most densely monitored objects hosting a $\sim$$10^9{M}_{\odot }$ 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 $\hat{I}“$ are also observed, questioning expectations from previously reported $\hat{I}“-\hat{I}{»}_{\mathrm{Edd}}$ relations, for which $\hat{I}“\ge 2$ would be a ubiquitous hallmark of AGN with $\hat{I}{»}_{\mathrm{Edd}}\sim 1$.

7 pages, 5 figures, proceedings of the XMM-Newton Workshop 2022 "Black hole accretion under the X-ray microscope". Accepted for publication in Astronomische Nachrichten