Constraining the power of X-ray winds: a Bayesian approach
Abstract
A key outstanding question in our understanding of AGN feedback is the physics of accretion-driven black hole outflows, which may be powerful enough to prevent the stars from forming. However, without precisely mapping the ionization, velocity, and, crucially, density structure of these highly ionized winds, we cannot constrain their impact on the host galaxy evolution. In this talk, I will introduce our improved Bayesian framework to characterizing X-ray detected AGN outflows, wherein the ionizing spectrum and wind absorption are treated self-consistently within an MCMC analysis. This provides substantial improvements in our ability to explore parameter space and to recover the covariance between the emission and absorption parameters. For the first time we are able to perform robust model selection, which allows us to discriminate between non-nested models and establish how many wind components are required by the data. We have successfully applied this approach to one of the deepest Chandra HETG observations of an AGN, a new 700 ks observation of NGC 4051. Within our framework we were able to select the most reliable continuum model, in particular the soft excess emission, and discriminate between the wind and hot Milky Way ISM absorption features present in high resolution spectra. This approach also utilizes density-sensitive line transitions (here, the Fe XXII doublet), enabling us to obtain one of the tightest wind density measurements to date. As a result, we could precisely constrain the location and kinetic power of the outflow in NGC 4051. Our future work will extend the analysis to a population study of the physical structure and duty cycles of disk winds in local AGN, and serve as a pathfinder for the upcoming high spectral resolution X-ray missions, including XRISM, Arcus, and ATHENA.
- Publication:
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AAS/High Energy Astrophysics Division
- Pub Date:
- March 2019
- Bibcode:
- 2019HEAD...1710622O