Long Term Reverberation Mapping of Iron Coronal Lines in MKN 110

TL;DR

This study analyzes long-term flux measurements of coronal iron lines in the AGN MKN 110, revealing stratification and spatial distribution within the coronal line region through lag detection and variability analysis.

Contribution

It provides the first long-term reverberation mapping of coronal lines in MKN 110, demonstrating stratification and complex structure of the coronal line region.

Findings

Detected a 652-day lag for [Fe VII] relative to the continuum

No significant lag detected for [Fe X] due to uncertainties

Evidence of a non-varying component in coronal line fluxes

Abstract

We present flux measurements of the coronal lines [Fe VII] and [Fe X] spanning three decades, in the highly variable Active Galactic Nucleus (AGN) MKN 110. These coronal lines are sensitive to the spectral energy distribution (SED) of AGNs in the extreme ultraviolet (EUV). Neither [Fe VII] nor [Fe X] demonstrates variability in the short term on a weekly or monthly timescale. However, by taking advantage of a long term decrease in the continuum flux of MKN 110 on the order of years, we were able to track the [Fe VII] and [Fe X] fluxes as they respond to the continuum. We were able to detect a lag for [Fe VII] relative to the continuum at 5100 {\AA}, with a modal lag of 652 days, but were unable to detect a significant lag in the [Fe x] flux, though there exist significant uncertainties in the [Fe X] fit. These two lag results are not consistent and the line widths for the two line species also do not match. This provides strong evidence for stratification within the coronal line region (CLR). There is also evidence of a non-varying component within the coronal line flux, probably a result of a more extended region of origin. Taken together, these results suggest a CLR where the bulk of the [Fe VII] originates on parsec scales, but a portion of the [Fe VII] flux originates further out, at or beyond a 10 pc scale. These results also indicate the limitations of single-cloud models in describing the physical conditions of the CLR.