Spatial linearity

Spatial linearity tests, including the effects of sub-pixel structure on that linearity, were conducted using the ACIS-2C instrument with the HRMA at XRCF. The tests were performed in two sessions with slightly different modes of operations.

In the first session both front- and back-illuminated chips of the ACIS-2C instrument have been used. They were exposed to the Cu K-alpha (8.04 keV) and O K-alpha (0.53 keV) photons.

The FAM was being moved in either horizontal (FAM Y) or vertical (FAM Z) directions with increments of 5 $\mu$m. At each position data were collected for 300 seconds, so that the total number of X-ray events detected was about 1000 for oxygen K-$\alpha$and about 300 for copper. The total motion of the FAM in both directions was 20-30 $\mu$m.

In the second session FAM steps were nominally 27 $\mu$m, which resulted in a total path of $\sim$440 $\mu$m in the horizontal direction and $\sim$300 $\mu$m in the vertical direction. This mode improved dramatically the FAM mechanical performance and repeatability of the data. The ACIS-2C front-illuminated chip was exposed to Mg K$_{\alpha }$(1.25 keV) and Mo L$_{\alpha }$ (2.29 keV) X-rays in this session, with 50 sec data collection at each step, so that the total number of detected events at each point was about 200.