Probing The Spatial Distribution Of The Interstellar Dust Medium By High Angular Resolution X-ray Halos Of Point Sources

X-rays are absorbed and scattered by dust grains when they travel through theinterstellar medium. The scattering within small angles results in an X-ray "halo". Thehalo properties are significantly affected by the energy of radiation, the optical depth ofthe scattering, the grain size distributions and compositions, and the spatial distributionof dust along the line of sight (LOS). Therefore analyzing the X-ray halo properties is animportant tool to study the size distribution and spatial distribution of interstellar grains,which plays a central role in the astrophysical study of the interstellar medium, suchas the thermodynamics and chemistry of the gas and the dynamics of star formation.With excellent angular resolution, good energy resolution and broad energy band, theChandra ACIS is so far the best instrument for studying the X-ray halos. But the directimages of bright sources obtained with ACIS usually suffer from severe pileup whichprevents us from obtaining the halos in small angles.We first improve the method proposed by Yao et al to resolve the X-ray dust scat-tering halos of point sources from the zeroth order data in CC-mode or the first or-der data in TE mode with Chandra HETG/ACIS. Using this method we re-analyzethe Cygnus X-1 data observed with Chandra. Then we studied the X-ray dust scat-tering halos around 17 bright X-ray point sources using Chandra data. All sourceswere observed with the HETG/ACIS in CC-mode or TE-mode. Using the inter-stellar grain models of WD01 model and MRN model to fit the halo profiles, weget the hydrogen column densities and the spatial distributions of the scattering dustgrains along the line of sights (LOS) to these sources. We find there is a good lin-ear correlation not only between the scattering hydrogen column density from WD01model and the one from MRN model, but also between NH derived from spectralfits and the one derived from the grain models WD01 and MRN (except for GX301-2 and Vela X-1): NH,WD01 = (0.720 ± 0.009) × N_H,abs + (0.051 ± 0.013) andN_H,MRN = (1.156 ± 0.016) × N_H,abs + (0.062 ± 0.024) in the units 10²² cm^-2. Thenthe correlation between FHI and NH is obtained. Both WD01 model and MRN modelfits show that the scattering dust density very close to these sources is much higher thanthe normal interstellar medium and we consider it is the evidence of molecular cloudsaround these X-ray binaries. We also find that there is the linear correlation betweenthe effective distance through the galactic dust layer and hydrogen scattering columndensity NH excluding the one in x = 0.99 ? 1.0 but the correlation does not exist be-tween he effective distance and the NH in x = 0.99?1.0. It shows that the dust nearbythe X-ray sources is not the dust from galactic disk. Then we estimate the structure anddensity of the stellar wind around the special X-ray pulsars Vela X-1 and GX 301-2.Finally we discuss the possibility of probing the three dimensional structure ofthe interstellar using the X-ray halos of the transient sources, probing the spatial dis-tributions of interstellar dust medium nearby the point sources, even the structure ofthe stellar winds using higher angular resolution X-ray dust scattering halos and testingthe model that the black hole can be formed from the direct collapse of a massive starwithout supernova using the statistical distribution of the dust density nearby the X-raybinaries.