The high background periods were excluded. The ratio of these spectra is shown in the bottom panel. This is shown in more detail in the section below. The spectrum of the central part of the cluster, excluding the piled-up nucleus is shown below. Background was subtracted using a region which was relatively free from the cluster emission.
Red crosses show the spectrum after cleaning.
The bottom panel shows the ratio of the clean and total spectra. The figure below shows the background spectrum in the source-free region in the S3 chip. The ratio of these spectra is shown in the bottom panel. This test case shows the rejection efficiency in the back-illuminated S3 chip. The spectrum of the cluster center is shown below.