Modelling the Extreme X-ray Spectrum of IRAS 13224-3809

TL;DR

This study analyzes the spectral variability of the NLS1 galaxy IRAS 13224-3809, using relativistic reflection models to explain its X-ray spectrum and revealing evidence of gravitational light-bending effects.

Contribution

It provides a detailed spectral analysis of IRAS 13224-3809, demonstrating the effectiveness of relativistic reflection models and identifying a thermal blackbody component consistent with accretion disc emission.

Findings

Relativistic reflection explains the time-averaged spectrum well.

Blackbody temperature and flux follow the L∝T⁴ relation.

Evidence of gravitational light-bending effects in flux-resolved spectra.

Abstract

The extreme NLS1 galaxy IRAS 13224-3809 shows significant variability, frequency depended time lags, and strong Fe K line and Fe L features in the long 2011 XMM-Newton observation. In this work we study the spectral properties of IRAS 13224-3809 in detail, and carry out a series of analyses to probe the nature of the source, focusing in particular on the spectral variability exhibited. The RGS spectrum shows no obvious signatures of absorption by partially ionised material (warm absorbers). We fit the 0.3-10.0 keV spectra with a model that includes relativistic reflection from the inner accretion disc, a standard powerlaw AGN continuum, and a low-temperature (~0.1 keV) blackbody, which may originate in the accretion disc, either as direct or reprocessed thermal emission. We find that the reflection model explains the time-averaged spectrum well, and we also undertake flux-resolved and time-resolved spectral analyses, which provide evidence of gravitational light-bending effects. Additionally, the temperature and flux of the blackbody component are found to follow the $L\propto T^{4}$ relation expected for simple thermal blackbody emission from a constant emitting area, indicating a physical origin for this component.