Extended Corona Models of X-ray Reverberation in the AGN 1H~0707-495 and IRAS 13224-3809

TL;DR

This study models X-ray reverberation in two AGN using an extended corona model with two sources, revealing correlations between corona height, spectral softness, and ionization over 16 years.

Contribution

Introduces a vertically extended two-source corona model to interpret X-ray reverberation data in AGN, linking spectral and ionization properties with corona geometry and dynamics.

Findings

Correlations between corona height and spectral softness.

Faster corona response associated with softer spectra.

Evidence of a more patchy, multi-zone corona in IRAS 13224-3809.

Abstract

We fit a new vertically extended corona model to previously measured reverberation time lags observed by \emph{XMM-Newton} in two extremely variable Narrow Line Seyfert 1 Active Galactic Nuclei (AGN), 1H~0707-495 and IRAS~13224-3809, in a variety of similarly observed flux groups and explore the model in all observations over a 16 year period. The model employs two X-ray sources located along the black hole rotational axis at height, $h_1$ and $h_2$ respectively. These sources have their associated photon indices $\Gamma_1$ and $\Gamma_2$ which respond to fluctuations in the disc with a maximum response duration of $t_\text{max}$ and a propagation delay between the response of the two of $t_\text{shift}$. We find that for 1H 0707-495, $h_2$ is significantly correlated with $\Gamma_1$ and anti-correlated with ionisation $\xi$. Whilst the 1H 0707-495 corona extends upwards, the emission appears softer and the disc is less ionised. We find similarities in IRAS 13224-3809, but significant anti-correlation between $\Gamma_2$ and both $t_\text{max}$ and $t_\text{shift}$. This suggests that when the IRAS 13224-3809 corona becomes softer while extending vertically upwards, the overall corona response occurs faster. This may also suggest that the inner disc also becomes more active. In addition, $\Gamma_1$ and $\Gamma_2$ are extreme, relatively less variable, but more separate in IRAS 13224-3809 than in 1H 0707-495. This suggests that the IRAS 13224-3809 corona may be more patchy in the sense that it has two more clear distinct spectral zones of $\Gamma_1$ and $\Gamma_2$ (possibly relating to two distinct zones of coronal temperature) when compared to 1H 0707-495.