A re--analysis of the iron line in the XMM-Newton data from the low/hard state in GX339--4

TL;DR

This paper re-analyzes XMM-Newton data of GX339-4's low/hard state, revealing that pileup affected previous broad iron line detections, and supports the truncated disc model with new PN timing mode data.

Contribution

It demonstrates that pileup significantly influenced earlier results and provides new timing mode analysis that aligns with the truncated disc interpretation.

Findings

Previous broad iron line detection was affected by pileup.

Timing mode data shows a narrower iron line.

Results support the truncated disc model for GX339-4.

Abstract

The detection of an extremely broad iron line in XMM-Newton MOS data from the low/hard state of the black hole binary GX339-4 is the only piece of evidence which unambiguously conflicts with the otherwise extremely successful truncated disc interpretation of this state. However, it also conflicts with some aspect of observational data for all other alternative geometries of the low/hard state, including jet models, making it very difficult to understand. We re-analyse these data and show that they are strongly affected by pileup even with extensive centroid removal as the source is ~200x brighter than the recommended maximum countrate. Instead, we extract the simultaneous PN timing mode data which should not be affected by pileup. These show a line which is significantly narrower than in the MOS data. Thus these data are easily consistent with a truncated disc, and indeed, strongly support such an interpretation.