By Michael L. Parker

There are two effects around AGN that can produce a relativistically broadened iron line profile: relativistic reflection (i.e. emission from the inner accretion disk), and ultra-fast outflows (powerful winds launched away from the disk). We want to study both of them with Athena because they give us powerful tools for understanding AGN formation and feedback and accretion physics. However, in practise, these two effects are spectrally indistinguishable, even with Athena, and we demonstrate this by simulating thousands of spectra with XMM-Newton and Athena and showing that both models can fit them equally well, regardless of the true model. This is pretty bad news because it means there's a huge systematic error in parameters estimated from either model if the other effect is also present. We then explore various ways that this degeneracy can be mitigated, such as using variability information to track light travel times or using high energy X-ray coverage to constrain the Compton hump emission.

The takeaway point is that there's a lot of work we need to do before Athena launches to make sure we can actually get reliable measurements out!

 Access to the manuscript in ADS.