Variability study of the High Mass X-ray Binary IGR J18027--2016 with {\it Swift}--XRT

TL;DR

This study analyzes the variability, pulsations, and spectral properties of the high-mass X-ray binary IGR J18027--2016 using Swift-XRT observations across different orbital phases, revealing significant flux changes and consistent pulsations.

Contribution

It provides detailed pulsation and spectral analysis of IGR J18027--2016 across various orbital phases, highlighting flux variability and potential causes like clumpy wind and hydrodynamic instabilities.

Findings

X-ray intensity varies by a factor of about 50 across orbital phases.

Pulsations around 140 seconds are consistently detected.

Spectral absorption is high before and after eclipse.

Abstract

We report the results from pulsations and spectral analysis of a large number of observations of the HMXB pulsar IGR J18027--2016 with {\it Swift}--XRT, carried out at different orbital phases. In some orbital phases, as seen in different XRT observations, the X-ray intensity is found to vary by a large factor, of about $\sim$50. In all the observations with sufficient number of source X-ray photons, pulsations have been detected around the previously known pulse period of $\sim$140 sec, When detected, the pulse profiles do not show any significant variation over a flux difference of a factor of $\sim$3. The absorption column density is found to be large before and after the eclipse. We discuss various possible reasons for intensity and spectral variations in IGR J18027--2016, such as clumpy wind and hydrodynamic instabilities.