Revealing the accretion disc corona in Mrk 335 with multi-epoch X-ray spectroscopy

TL;DR

This study analyzes multi-epoch X-ray spectra of Mrk 335 to reveal how the accretion disc and corona properties change with accretion rate, showing correlations between ionization, spectral cut-off, and corona geometry.

Contribution

It provides new insights into the correlation between Eddington ratio and spectral parameters, revealing geometrical changes of the corona with accretion rate in Mrk 335.

Findings

Ionization parameter correlates strongly with Eddington ratio.

The spectral cut-off energy increases with Eddington ratio.

Reflection fraction decreases as the accretion rate increases.

Abstract

Active galactic nuclei host an accretion disc with an X-ray producing corona around a supermassive black hole. In bright sources, such as the Seyfert 1 galaxy Mrk 335, reflection of the coronal emission off the accretion disc has been observed. Reflection produces spectral features such as an iron emission line, which allow for properties of the inner accretion disc and the corona to be constrained. We perform a multi-epoch spectral analysis of all XMM-Newton, Suzaku, and NuSTAR observations of Mrk 335, and we optimize our fitting procedure to unveil correlations between the Eddington ratio and the spectral parameters. We find that the disc's ionization parameter correlates strongly with the Eddington ratio: the inner disc is more strongly ionized at higher flux. The slope of the correlation is less steep than previously predicted. Furthermore, the cut-off of the power-law spectrum increases in energy with the Eddington ratio, whereas the reflection fraction exhibits a decrease. We interpret this behaviour as geometrical changes of the corona as a function of the accretion rate. Below ~10% of the Eddington limit, the compact and optically thick corona is located close to the inner disc, whereas at higher accretion rates the corona is likely optically thin and extends vertically further away from the disc surface. Furthermore, we find a soft excess that consists of two components. In addition to a contribution from reflection in low ionization states, a second component is present that traces the overall flux.