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Small angle scattering by dust grains causes a significant contribution tothe total interstellar extinction for any X-ray instrument with sub-arcminuteresolution (Chandra, Swift, XMM-Newton). However, the dust scattering componentis not included in the current absorption models: phabs, tbabs, and tbnew. Wesimulate a large number of Chandra spectra to explore the bias in the spectralfit and NH measurements obtained without including extinction from dustscattering. We find that without incorporating dust scattering, the measured NHwill be too large by a baseline level of 25%. This effect is modulated by theimaging resolution of the telescope, because some amount of unresolvedscattered light will be captured within the aperture used to extract pointsource information. In high resolution spectroscopy, dust scatteringsignificantly enhances the total extinction optical depth and the shape of thephotoelectric absorption edges. We focus in particular on the Fe-L edge at 0.7keV, showing that the total extinction template fits well to the highresolution spectrum of three X-ray binaries from the Chandra archive: GX 9+9,XTE J1817-330, and Cyg X-1. In cases where dust is intrinsic to the source, acovering factor based on the angular extent of the dusty material must beapplied to the extinction curve, regardless of angular imaging resolution. Thisapproach will be particularly relevant for dust in quasar absorption linesystems and might constrain clump sizes in active galactic nuclei.

The dust scattering component of X-ray extinction: Effects on continuum fitting and high-resolution absorption edge structure