A Chandra View of the GRB221009 Dust Echo as a Probe of Galactic Structure

Because of its low Galactic latitude of 4.25 degrees, the exceptionally bright X-ray counterpart of GRB221009A produced a bright dust scattering ring echo off a number of intervening dust clouds. The essentially infinite distance of the X-ray source allow geometric distance measurements to each cloud with unprecedented accuracy. We will present Chandra data of the echo (the highest resolution data available of the rings) and will discuss important new constraints they place on Galactic structure.