DETERMINING THE DISTANCE OF Cyg X-3 WITH ITS X-RAY DUST SCATTERING HALO

Using a cross-correlation method, we study the X-ray halo of Cyg X-3. Two components of dust distributions are needed to explain the time lags derived by the cross-correlation method. Assuming the distance as 1.7 kpc for Cyg OB2 association (a richest OB association in the local Galaxy) and another uniform dust distribution, we get a distance of 7.2(-0.5)(+0.3) kpc (68% confidence level) for Cyg X-3. When using the distance estimation of Cygnus OB2 as 1.38 or 1.82 kpc, the inferred distance for Cyg X-3 is 3.4(-0.2)(+0.2) or 9.3(-0.4)(+0.6) kpc, respectively. The distance estimation uncertainty of Cyg X-3 is mainly related to the distance of the Cyg OB2, which may be improved in the future with high-precision astrometric measurements. The advantage of this method is that the result depends weakly on the photon energy, dust grain radius, scattering cross-section, and so on.