Investigating a unique partial eclipse in the High Mass X-ray Binary IGR J16393-4643 with Swift-XRT

TL;DR

This study uses Swift-XRT observations to analyze a partial, narrow dip in the X-ray emission of IGR J16393-4643, suggesting it is caused by stellar corona absorption rather than an eclipse.

Contribution

It provides detailed phase-resolved spectroscopy and proposes a new interpretation of the low intensity phase as absorption, not an eclipse, in a high mass X-ray binary.

Findings

The low intensity phase is about 30% of the normal emission.

Spectral analysis indicates absorption in the stellar corona.

Inclination angle suggests a grazing eclipse scenario.

Abstract

The orbital profile of the High Mass X-ray binary IGR J16393-4643 shows a dip in its X-ray intensity, which was previously interpreted as an eclipse. Unlike most eclipsing HMXBs, where the X-ray eclipses are about two orders of magnitude fainter compared to the out of eclipse emission, this particular eclipse like feature is narrow and partial, casting doubt if it is indeed an eclipse. To further investigate the nature of this low intensity orbital phase, we use a large number of observations with Swift-XRT, covering the entire orbital phase. The soft X-ray observations also show this low intensity phase, which is about 30% of the intensity during rest of the orbit. We also carried out orbital phase resolved spectroscopy to compare the change in the spectral parameters inside and outside of this low intensity state. The results indicate that this low intensity state might not be an eclipse, as previously thought but absorption in the stellar corona. We have also provided the inclination angle of the binary for grazing eclipse caused by the stellar corona.