Variability study of the High Mass X-ray binary IGR J18027-2016 with Swift -XRT

We report the results from pulsations and spectral analysis of a large number of observations of the high-mass X-ray binary pulsar IGR J18027-2016 with Swift X-ray Telescope (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 similar to 50. In all the observations with sufficient number of source X-ray photons, pulsations have been detected around the previously known pulse period of similar to 140 s. When detected, the pulse profiles do not show any significant variation over a flux difference of a factor of similar to 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.