The effect of mirror curvature and wedging on the angular resolution of Athena

ESA’s Athena mission will use silicon pore optics, in which the optics assembly consists of pairs of mirror plates stacked into mirror modules. This paper presents a study of the angular resolution of Athena, using several candidate variants of mirror curvature and wedging. Results were achieved by ray-tracing these variants of Athena’s optics with the ray-tracing software SPORT.

The study shows that all polynomial variants yield a PSF below 1” on-axis, at all energies between 0.1 and 12 keV. The secondary-only polynomial variants perform best, for both on- and off-axis point sources. Of these variants, the wedging 0/2 variant is shown to generally yield superior angular resolution at higher energies, the -1/1 variant at lower energies.

A ray-tracing analysis using the Crab Nebula as an observation target was also performed. A 2D Fourier analysis was applied to the resulting focal plane responses to determine their angular resolution. This analysis indicates the angular resolution of all polynomial variants to be below 1”, at all but the highest energies.

It also shows, though to a lesser extent, that the secondary-only polynomial variants perform best in most circumstances. Nevertheless, this second analysis requires further investigation for a more conclusive outcome.