X-ray halos as diagnostics of interstellar grains

Abstract

Interstellar grains scatter X-rays from point sources into an observable halo surrounding the source image. Attention is presently given to the scattering of various grain-size distributions, both for halos around point sources and the cases of a source occulted by the moon. The limitations associated with using the X-ray halo to ascertain the size distribution of grains. The distribution of dust along the line-of-sight is noted to affect the inner part of the halo, rendering it more peaked toward the central point source if the dust is concentrated near the source.