Dust Busters: The Effects of Dust Scattering on Observations of X-Ray Binaries

In my project, I will improve upon a computational model of the light emitted from blackhole x-ray binaries. X-ray binaries are two stars closely orbiting each other, where one is usually a black hole. The 'donor' star gives off matter to the black hole, thereby releasing lots of light. We can observe these x-ray binaries with x-ray telescopes such as SWIFT/XRT. By fitting models to the observed spectrum of the binary, we can find out properties of the black hole such as the spin. Currently, these models account for the light emitted by the accretion disk (a disk of matter that swirls around the black hole), the light emitted by the corona (an area of plasma outside of the accretion disk), and the fact that dust in between us and the binary absorbs some of the light. However, with the exception of one, these models fail to recognize that some light can be scattered into the telescope by the dust. The exception to this, named XSCAT, however, does not account for the properties of how SWIFT/XRT makes these observations. This generally leads to an overestimate of the black hole's spin, which is very important to know in general relativity. To correct this, I will develop a program that accounts for off-center sources and rectangular extraction regions which are intrinsic to SWIFT/XRT's observations.