The Variable Relativistic Outflow of IRAS 13224-3809

TL;DR

This study re-analyzed XMM-Newton data of IRAS 13224-3809, confirming an ultrafast outflow with variable velocity that correlates with flux, and clarified previous findings by addressing background contamination issues.

Contribution

The paper presents a revised analysis of the ultrafast outflow in IRAS 13224-3809, revealing velocity variability and flux correlation, correcting prior background-related biases.

Findings

Outflow velocity varies from ~0.2c to ~0.3c.

Outflow velocity increases with 3-10 keV flux.

Anti-correlation between iron line equivalent width and flux disappears.

Abstract

The discovery of an ultrafast outflow has been reported in the z=0.0658 narrow line Seyfert galaxy IRAS 13224-3809 (Parker et al. 2017a). The ultrafast outflow was first inferred through the detection of highly blueshifted absorption lines (Parker et al. 2017a) and then confirmed with a principal component analysis (PCA) (Parker et al. 2017b). Two of the reported properties of this outflow differed from those typically detected in other AGN with ultrafast outflows. First, the outflow velocity was found not to vary with v=0.236c +/- 0.006c. Second, the equivalent width of the highly blueshifted absorption line was reported to be anti-correlated with the 3-10 keV flux of this source. We present a re-analysis of the XMM-Newton observations of IRAS 13224-3809 considering the influence of background. We also undertook a different analysis approach in combining the spectra and investigated the change of the properties of the outflow as a function of 3-10 keV flux and time. We confirm the presence of an ultrafast outflow in IRAS 13224-3809, however, we find that the background spectra used in the Parker et al. analyses dominate the source spectra for energies near the blueshifted iron lines. By reducing the source extraction regions to improve the signal-to-noise ratio we discover larger than previously reported outflow velocities and find that the outflow velocity varies from ~0.2c to ~0.3c and increases with 3-10~keV flux. The previously reported anti-correlation between equivalent width of the iron line and 3-10 keV flux disappears when the background spectra are reduced by optimizing the source extraction regions.