Dust Scattering Halos with Chandra Observations of Cygnus X - 3 and Cygnus X - 1

We improve the method proposed by Yao et al (2003) to resolve the X-ray dust scattering halos of point sources. Using this method we re-analyze the Cygnus X-1 data observed with Chandra (ObsID 1511) and derive the halo radial profile in different energy bands and the fractional halo intensity (FHI) as I(E) = 0.402×E keV. We also apply the method to the Cygnus X-3 data (Chandra ObsID 425) and derive the halo radial profile from the first order data with the Chandra ACIS+HETG. It is found that the halo radial profile could be fit by the halo model MRN (Mathis, Rumpl & Nordsieck, 1977) and WD01 (Weingartner & Draine, 2001); the dust clouds should be located at between 1/2 to 1 of the distance to Cygnus X-1 and between 1/6 to 3/4 (from MRN model) or 1/6 to 2/3 (from WD01 model) of the distance to Cygnus X-3, respectively.