CXO Project Science: X-ray opacity maps from HRC-I +Z vertex

Images display 60-keV x-ray absorption depth (forward hemisphere directional cosine), as viewed from the HRC-I +Z vertex (worst-case location). The left panel includes attenuation by the existing focus-structure baffle; the right panel omits it. The color scale is logarithmic, ranging from a 60-keV absorption depth of 0.01 (red) to 10 (blue). Because x-ray absorption is roughly inversely proportional to the cube of the photon energy, an absorption depth 0.04 (red-orange) at 60 keV corresponds to about 1 at 20 keV.

Note that the focus-structure shielding fills gaps in coverage by the HRC snout. To evaluate more quantitatively the coverage afforded by this shielding, compare the opacity probability distributions as viewed from HRC-I +Z vertex.

HRC-I +Z vertex, during HRC-I observation

With the focus-structure tantalum, less than 0.01 steradian is transparent down to about 20 keV; without it, 0.03 steradian is. Thus the additional 20-keV coverage afforded by this shielding is only 0.2% of the sky.

HRC-I +Z vertex, during ACIS-S observation

With the focus-structure tantalum, 0.3 steradian is transparent down to about 20 keV; without it, 0.4 steradian is. Thus, with or without this shielding, the 20-keV coverage has a gap of about 3% of the sky.

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