Time Variability and Ghost Halos
Dust grains polluting the intergalactic medium (IGM) have a chance of being detected through the phenomenon of X-ray scattering, which produces a diffuse arcminute-scale halo around bright X-ray point sources. I present follow up work to Corrales & Paerels (2012) by calculating the expected intensity of intergalactic dust scattering halos using the more exact Mie scattering treatment. This adjustment is necessary to check for large 0.1-1 micron sized dust grains that would interfere with the photometry needed for high precision measurements of cosmological constants. Even with the supreme focusing power of Chandra, I find that the dust scattering halo intensity is much dimmer than the Chandra PSF wings. However, scattered light takes a longer path to reach the observer, causing intergalactic scattering halos to be delayed ~10,000 years. I investigate the possibility of detecting a scattering halo around a quasar that has recently become dim, or ghost halos from a past quasar that is no longer visible.