Effective Area and Telescope Vignetting

Measurements of on-axis effective areas at energies of 6.627, 8.837, and 11.046 keV, integrated over a 105$^{\prime}$ diameter field of view, indicate that the actual effective area is only $\sim$65% of that predicted from ray-tracing studies of an ideal telescope with the SODART design parameters. These results are shown in Figure 17. It is believed that a significant fraction of this effective area reduction is due to the imperfect shape of individual foils near quadrant boundaries.

The relative reduction in effective area for off-axis sources (telescope vignetting) is shown in Figure 18.