空间X射线观测确定脉冲星星历表参数精度分析

脉冲星星历表维持着脉冲星导航所需的时空基准, 其精度直接影响着航天器导航定位结果, 是脉冲星导航系统的基本要素. 本文分析了脉冲星空间观测精度的估计方法, 探索性地研究了基于空间X射线观测获取星历表参数的可行性. 通过建立星历表参数拟合模型, 采用大样本重复事件仿真分析了空间X射线观测精度, 研究了星历表参数确定精度与观测精度、观测时间及观测频次的关系. 研究结果表明, 空间X射线观测可以确定脉冲星星历表参数, 但受限于脉冲星信号特征及探测器技术水平, 当前高精度导航用脉冲星星历表难以通过空间X射线观测手段获得, 可通过地面射电观测技术较好地建立与维持, 提出了推进我国大口径射电望远镜建设的建议.

Analysis of measurement accuracy of ephemeris parameters for pulsar navigation based on the X-ray space observation

The pulsar ephemeris that maintains the time-space benchmark for pulsar navigation is an important part of Xray pulsar navigation system. The parameters of pulsar timing model which are contained in the pulsar ephemeris can influence directly the accuracy of pulsar navigation. Some studies have shown that 100 m target of X-ray pulsar navigation should need 1 mas angle position and 100 ns pulse time of arrival, the high-level precision of parameters of some pulsars can be reached by ground radio observations with large-diameter telescope. Owing to the development of high-performance X-ray detector and stable space observation platform, the technology that the parameters of pulsar ephemeris are measured by space X-ray observations may be achieved, so the feasibility of this technology is studied in this paper by reconstructing the analysis process. The process includes mainly three parts. Firstly, the methods of simulating X-ray pulsar signals, replicating pulse profile and getting the time of arrival between the observed pulse profile and the standard one from analyzing observation data of the RXTE and Chandra satellite are studied, then the accuracies of X-ray space observations for four pulsars are estimated by using the large sample duplication events. Secondly, the process of fitting model for ephemeris parameters is established and realized by computer program in C++ language. Finally, the relationships between the accuracies of ephemeris parameters and those of the following factors are analyzed: the observation accuracy, the observation duration, the observed frequency. Those results of four pulsars (Crab, B1937+21, B1821-24 and B1509-58) are concluded below. 1) The X-ray space timing precisions of Crab pulsars in the observation durations of 1000 s and an hour are 1.41 s and 0.83 s respectively, the ones of other 3 pulsars in three different observation durations of 1000 s, an hour, and a day are also gained. 2) The ephemeris parameters of four pulsars are achieved by the X-ray space simulation observations, which are similar to the result of ground pulsar radio timing, the precision of right ascension is better than that of declination. 3) The precisions of ephemeris parameters can be improved by increasing the times of observation. 4) If each pulsar can be observed for 1000 s by space satellite every half an month with a 1 m² effective area detector, the precisions of the estimated parameters (RA, DEC and Period) for Crab pulsar are 23.4 mas 806.0 mas, 8.1213×10^-8 s, those of other three pulsars are gained and analyzed. However, owing to the low-flux radiation characteristics of millisecond X-ray pulsar and the demand for light and efficient large detector, the high-precision ephemeris parameters can be achieved difficultly by using the space X-ray observations, but can be established and maintained well by the ground radio observation technology. The suggestion for promoting the construction of some large-diameter telescopes is made, and the method that the behavior of X-ray emissions from pulsar is predicted by the ground radio observations still needs be studied.