Using the X-ray Dust Scattering Halo of Cygnus X-1 to determine distance and dust distributions

TL;DR

This study uses X-ray dust scattering halos observed by Chandra to determine the distance to Cygnus X-1 and map dust distributions, revealing a dense cloud at 1.6 kpc and refining the source distance to 1.81 kpc.

Contribution

It introduces a new dust model (XLNW) and combines halo profiles and lightcurves to accurately estimate the distance and dust distribution along the line of sight to Cygnus X-1.

Findings

Distance to Cygnus X-1 is 1.81 kpc with 0.09 kpc uncertainty.

A dense dust cloud contributes ~50% of dust at 1.6 kpc.

Most dust along the line of sight is near the black hole binary.

Abstract

We present a detailed study of the X-ray dust scattering halo of the black hole candidate \cygx1 based on two \chandra\ HETGS observations. Using 18 different dust models, including one modified by us (dubbed XLNW), we probe the interstellar medium between us and this source. A consistent description of the cloud properties along the line of sight that describes at the same time the halo radial profile, the halo lightcurves, and the column density from source spectroscopy is best achieved with a small subset of these models. Combining the studies of the halo radial profile and the halo lightcurves, we favor a geometric distance to \cygx1 of $d=1.81\pm{0.09}$\,kpc. Our study also shows that there is a dense cloud, which contributes $\sim$50% of the dust grains along the line of sight to \cygx1, located at $\sim1.6$ kpc from us. The remainder of the dust along the line of sight is close to the black hole binary.