Effects of Interstellar Dust Scattering on the X-ray Eclipses of the LMXB AX J1745.6-2901 in the Galactic Center

AX J1745.6-2901 is an eclipsing low mass X-ray binary (LMXB) in the Galactic Centre. It shows significant X-ray excess emission during the eclipse phase, and its eclipse light curve shows an asymmetric shape. We use archival XMM-Newton and Chandra observations to study the origin of this peculiar X-ray eclipsing phenomena. We find that the shape of the observed X-ray eclipse light curves depends on the instrumental point-spread-function (PSF), source extraction region and photon energy. By performing detailed simulations for the time-dependent X-ray dust scattering halo, we find that an eclipsing X-ray source sitting behind a significant amount of interstellar dust should show special eclipse light curves of asymmetric shape. By directly modelling the observed eclipse and non-eclipse halo profiles of AX J1745.6-2901, we obtained solid evidence that its peculiar eclipse phenomena are indeed caused by the X-ray dust scattering in multiple dust layers along the line-of-sight (LOS). Our results can be used to justify the effect of dust scattering in other eclipsing X-ray sources. Moreover, our halo eclipse study reinforces the existence of a dust layer local to AX J1745.6-2901 as reported by Jin et al. (2017), as well as identifying another dust layer within a few hundred parsecs to the Earth, containing up to several tens of percent LOS dust, which is likely to be associated with the molecular clouds in the Solar neighbourhood. The remaining LOS dust is likely to be associated with the molecular clouds located in the Galactic disk in-between.