SIMBAD references

We report the results from pulsations and spectral analysis of a large number of observations of the HMXB pulsar IGR J18027–2016 with 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 ∼50. In all the observations with sufficient number of source X-ray photons, pulsations have been detected around the previously known pulse period of ∼140 sec, When detected, the pulse profiles do not show any significant variation over a flux difference of a factor of ∼ 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.