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