Revealing the Evolving Accretion Disk Corona in AGNs with Multi-Epoch X-ray Spectroscopy: the case of Mrk 335
Abstract
Active galactic nuclei host an accretion disk 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 disk has been observed. Reflection produces numerous spectral features, such as the Fe Kα emission line and absorption edge, which allow various properties of the inner accretion disk and corona to be constrained. We perform a multi-epoch spectral analysis of a dozen XMM-Newton, Suzaku, and NuSTAR observations of Mrk 335, and optimize the fitting procedure to unveil correlations between the Eddington ratio and multiple spectral parameters. We find that the ionization parameter of the accretion disk correlates strongly with the Eddington ratio: the inner disk is more strongly ionized at higher flux. Interestingly, 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 disk, whereas at higher accretion rates the corona is likely optically thin and extends vertically further away from the disk surface. Compared to previous work that considered individual spectra, we find that multi-epoch spectroscopy is essential for breaking degeneracies in the spectral fits and for obtaining accurate spectral parameters. Furthermore, we show that this method provides a powerful tool to study coronal evolution. The rich archives of XMM-Newton, Suzaku, and NuSTAR provide the opportunity to extend this investigation to include several other bright AGN, which will reveal whether the behaviour that we found is common or unique to Mrk 335.
- Publication:
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AAS/High Energy Astrophysics Division #15
- Pub Date:
- April 2016
- Bibcode:
- 2016HEAD...1510612B