A search for an X-ray scattering halo around Scorpius X-1

Results are presented of an experiment to detect the presence of X-ray scattering by interstellar dust grains in the form of a halo around Sco X-1. We utilized the principle that X-ray scattering off an optical is reduced by 1/sin θ for reflections out of the plane of incidence, thus reducing instrumental scattering off our moderate quality (1 arcminute) X-ray optic. We find an upper limit X-ray flux from Sco X-1 in the form of a halo at a mean energy of 0.69 keV of 7.6% of the point source flux at the 1 σ confidence level. From this we derive an upper limit of E(B- V) = 0.12 towards Sco X-1. This is about half the value [E(B-V) ∼0.3] derived toward Sco X-1 using the 2200 Å interstellar absorption feature, indicating probable circumstellar origin to the 2200 Å feature.