Onboard catalog of known X-ray sources for EP-WXT

He-Yang Liu; Haiwu Pan; Yuan Liu; Hong-Bo Cai; Yuyin Tan; Haitao Xu; Changbin Xue; Xiaojin Sun; Yifan Chen; Zhiwei Cheng; Ying Li; Yulong Xue; Huaqing Cheng; Xuan Mao; Zhixing Ling; Chen Zhang; Weimin Yuan

arXiv · 2607.17307

Onboard catalog of known X-ray sources for EP-WXT

He-Yang Liu·Haiwu Pan·Yuan Liu·Hong-Bo Cai·Yuyin Tan·Haitao Xu·Changbin Xue·Xiaojin Sun·Yifan Chen·Zhiwei Cheng·Ying Li·Yulong Xue·Huaqing Cheng·Xuan Mao·Zhixing Ling·Chen Zhang·Weimin Yuan

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Abstract

The Einstein Probe (EP) is dedicated to explore the dynamic X-ray universe and capture transient events in real time with its Wide-field X-ray Telescope (WXT). However, WXT's unprecedentedly large instantaneous field of view, exceeding 3,600 square degrees, simultaneously encompasses numerous known X-ray emitters. Distinguishing genuine novel transients from these persistent sources is a critical observational challenge. To resolve this, EP-WXT incorporates a dedicated reference catalog of known X-ray sources directly into its onboard data processing and triggering system. In this paper, we detail the compilation of this onboard catalog. By merging data from the ROSAT All Sky Survey, the MAXI source list, and a curated stellar flare candidate catalog, we constructed a robust baseline database of 9,000 sources. This catalog provides coordinates, baseline count rates, and spatial veto radii for exceptionally bright emitters. Real-time cross-matching against this database effectively decouples known background sources from the transient alert stream. Recent in-orbit operations validate the high stability and efficiency of this catalog-driven trigger system. Notably, the catalog successfully masked over 6,100 potential triggers from known active stars. This proves its essential role in ensuring EP's rapid and accurate response to genuine astrophysical discoveries.

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He-Yang Liu, Haiwu Pan, Yuan Liu, Hong-Bo Cai, Yuyin Tan, Haitao Xu, Changbin Xue, Xiaojin Sun, Yifan Chen, Zhiwei Cheng, Ying Li, Yulong Xue, Huaqing Cheng, Xuan Mao, Zhixing Ling, Chen Zhang, Weimin Yuan. 2026-07-19. Onboard catalog of known X-ray sources for EP-WXT. https://arxiv.org/abs/2607.17307

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