Particle-induced background rejection method for the follow-up X-ray telescope onboard Einstein probe

PurposeBackground removal is an important issue in data reduction for the follow-up X-ray telescope (FXT) onboard the Einstein Probe (EP), particularly for the particle-induced background. They appear in various charge patterns in the focal plane PN-CCD, such as straight tracks, isolated showers and broad rectangular swathes.
MethodsWe use the data obtained with the FXT mirror assembly covered, which are due to particle-induced background, to study the methods for rejecting such background.
ResultsThe particle-induced background in the FXT comprises background directly caused by particles, as well as instrument events that are also due to particles. A new rejection method, which involves cluster identification, and threshold veto for number of hits in rows and columns, is applied to remove the particle-induced background. The remaining background can be eliminated by the event reconstruction algorithm and event veto in subsequent FXT data reduction.
ConclusionIt is shown that their methods can achieve a background rejection efficiency of 99.8 %. Additionally, there has been a notable decrease in the number of spikes in the light curves of the FXT. Furthermore, we found the instrument background is attributed to a combination of particles and CAMEX electronics.