How the X-ray filters aboard the Einstein Probe were calibrated prior to launch
DOI: 10.1063/10.0039491
How the X-ray filters aboard the Einstein Probe were calibrated prior to launch lead image
On January 9, 2024, the Einstein Probe X-ray telescope was blasted into space to discover inactive black holes, detect neutron star mergers, and monitor variable objects. After detecting a transient event with its Wide-Field X-ray Telescope, further observations are made with its Follow-up X-ray Telescope (FXT).
Before launch, Xu et al. conducted comprehensive calibrations of the filters on FXT. The two optical and detector systems of FXT, mirror modules FXT-A and FXT-B, are each equipped with a rotating wheel of three types of filters with different transmittance at various energies.
“Ground calibration is a prerequisite for satellites to perform reliable scientific observations,” said author Jingjing Xu. “Only with accurate ground calibration results can we obtain rich scientific observational outcomes.”
To test the filters, the researchers used a specialized facility to target FXT with X-ray photons. FXT was positioned at one end of a 100-meter long vacuum pipe in a vacuum chamber, and a multi-target source at the other end of the pipe emitted X-rays photons that formed a quasi-parallel beam of light.
The transmittance of three different filters was tested and compared to a filter-free control. Using that data, they simulated a complete transmittance curve as a function of energy. Then, the real thickness of the filter was confirmed with the results of the transmittance curve.
“Test data validation indicates that the optical transmittance performance metrics closely align with the expected design values and simulation results, fully meeting the precision requirements of the FXT scientific observation mission,” Xu said.
This study lays the groundwork for testing the transmittance calibration of future filters. The calibration results can also be used to optimize design parameters for the next generation of filters.
Source: “Filter transmittance calibration of the follow-up X-ray telescope on board the EP satellite,” by Jingjing Xu, Juan Zhang, Tianxiang Chen, Na Gao, Xiaofan Zhao, Zijian Zhao, Weiwei Cui, Juan Wang, Yusa Wang, Yuxuan Zhu, Yanji Yang, Laidan Luo, Dawei Han, Jia Ma, Hao Wang, Xiongtao Yang, Jia Huo, Wei Li, Zhiliang Zhang, Haoyang Geng, Yong Chen, AIP Advances (2025). The article can be accessed at https://doi.org/10.1063/5.0254738 .
