Presentation #100.65 in the session AGN.
The discovery of energetic ultra-fast outflows (UFOs) in luminous active galactic nuclei (AGN) via the detection of highly blueshifted absorption lines in the X-ray count spectra is considered to provide the ‘feedback’ mechanisms linking the central supermassive black holes with their host galaxies. To characterize UFOs, we traditionally perform photoionization modeling of the observed absorption lines using X-ray flux spectra. However, the detection significance of UFO features strongly depends on the model used for the continuum. To overcome this issue, we developed a variability technique for advancing the detection of UFOs and created physical models to fit variability spectra. Our variability method of UFO detection is fast and less biased by the continuum shape. The UFO features appear as positive ‘spikes’ since they respond rapidly to the central X-ray source and are more pronounced than in traditional flux spectra. By fitting a simple spline to the variability spectra of a sample of bright AGN, we detected several UFO spikes of velocity 0.1-0.3c, unlike the flux spectra, which did not always show strong UFO absorption lines. This coherent UFO variability gives us a powerful probe of outflows in a whole new dimension. We also created physical models to fit the variability spectra of the sample and confirmed the presence of wind absorption (e.g., FeXXV or FeXXVI) outflowing with velocities 0.1-0.3c. Our variability models can constrain parameters inaccessible through conventional flux spectroscopy, such as the correlations between the wind and the accretion disk and the response time of the gas. One of the most important applications of such methods/models would be on X-ray microcalorimeter data from XRISM and Athena, where we can separate different layers of absorption in the wind with distinct variability properties.