Indication of the Less-ionized Clumpy Ultra-Fast Outflows in Seyfert Galaxies

TL;DR

This study reveals that clumpy, mildly ionized outflows in Seyfert galaxies exhibit velocities comparable to ultra-fast outflows, with variability linked to central X-ray flux, supporting a radiative-driven wind model.

Contribution

It introduces a spectral-ratio model fitting technique to analyze clumpy absorbers and demonstrates their connection to UFOs in Seyfert galaxies, a novel approach in this context.

Findings

Clumpy absorbers' outflow velocities are similar to UFOs.

Soft X-ray variability is mainly due to partial covering fluctuations.

Positive correlation between outflow velocities and X-ray fluxes.

Abstract

We present a systematic investigation of X-ray spectral variability of Seyfert 1 galaxies using a ``spectral-ratio model fitting'' technique, which we developed to estimate contribution of the putative clumpy absorbers to the spectral variations. Archival XMM-Newton observations of 12 active galactic nuclei were analyzed to constrain properties of these absorbers. Our analysis demonstrates that the soft X-ray variability is primarily governed by fluctuation of the partial covering fraction of mildly ionized clumpy clouds. In particular, for Mrk 335, PDS 456, and 1H 0707-495, outflow velocities of the clumpy absorbers are constrained from the blue-shifts of the Fe-L edge structure. The blue-shifted Fe-L edge successfully reproduces the well-known complex spectral feature near 1 keV in 1H 0707--495, which was often explained by invoking an ad hoc absorption structure. Notably, the inferred outflow velocities of the clumpy absorbers are comparable to, or even exceed, those associated with the Ultra-Fast Outflows (UFOs). Furthermore, we found a positive correlation between the outflow velocities and the intrinsic X-ray fluxes in two of four data sets, and the remaining two datasets also agree with this positive correlation, which supports a radiative-driven wind scenario that the X-ray/UV emission from the central black holes is causing the UFOs and the outflowing clumpy absorbers. In addition, the line-driven acceleration is likely playing a significant role, since the line opacities of the clumpy absorbers are highly sensitive to the flux changes. These findings provide a robust observational support for the ``hot inner and clumpy outer wind'' paradigm, suggesting a common origin for both the UFOs and the clumpy absorbers.