Investigating the X-ray time-lags in PG 1244+026 using an extended corona model

TL;DR

This paper introduces an extended corona model using ray-tracing simulations to analyze X-ray time lags in AGN PG 1244+026, revealing the geometry and dynamics of the corona and disc through timing data fitting.

Contribution

The study develops a novel extended corona model with two sources and demonstrates its ability to reproduce observed X-ray lag features in PG 1244+026.

Findings

Identified the locations of X-ray sources at ~6r_g and ~11r_g.

Reproduced both low-frequency hard and high-frequency soft lags.

Suggested the presence of a relativistic jet or outflowing blob.

Abstract

We present an extended corona model based on ray-tracing simulations to investigate X-ray time lags in Active Galactic Nuclei (AGN). This model consists of two axial point sources illuminating an accretion disc that produce the reverberation lags. These lags are due to the time delays between the directly observed and reflection photons and are associated with the light-travel time between the source and the disc, so they allow us to probe the disc-corona geometry. We assume the variations of two X-ray sources are triggered by the same primary variations, but allow the two sources to respond in different ways (i.e. having different source responses). The variations of each source induce a delayed accretion disc response and the total lags consist of a combination of both source and disc responses. We show that the extended corona model can reproduce both the low-frequency hard and high-frequency soft (reverberation) lags. Fitting the model to the timing data of PG~1244+026 reveals the hard and soft X-ray sources at $\sim6r_{\text{g}}$ and $\sim11r_{\text{g}}$, respectively. The upper source produces small amounts of reflection and can be interpreted as a relativistic jet, or outflowing blob, whose emission is beamed away from the disc. This explains the observed lag-energy in which there is no soft lag at energies $<1$~keV as they are diluted by the soft continuum of the upper source. Finally, our models suggest that the fluctuations propagating between the two sources of PG~1244+026 are possible but only at near the speed of light.