一种新的X射线脉冲星信号模拟方法

A new simulation method of X-ray pulsar signals

由于无法在地面直接观测到X射线脉冲星信号,且空间飞行探测耗时长,成本高,模拟具有真实物理特征的X射线脉冲星信号对X射线脉冲星信号处理方法及导航方案的验证具有重要意义.本文提出了一种利用太阳系质心处脉冲星信号模型和航天器轨道信息,建立航天器处实时光子到达速率函数,再利用尺度变换法产生光子到达时间序列的脉冲星信号模拟新方法.该方法真实还原了脉冲星信号的频率缓变特性,考虑了动态探测环境下的相对论效应,且避免了现有模拟航天器处光子序列方法中的迭代过程,产生非齐次泊松光子到达时间序列的运算量也低于常用的齐次泊松过程筛选法和反函数递推法.数值仿真从频率特性、流量特性、轮廓相似度及与实测数据的接近程度四个方面验证了该模拟方法的正确性.

Since X-ray pulsar signals cannot be directly detected on the ground, and the space flight detection is both timeconsuming and costly, simulation of X-ray pulsar signals with true physical characteristics is of great importance to the validation of various X-ray pulsar signal processing algorithms and X-ray pulsar-based navigation strategies. In this paper, a new simulation method of X-ray pulsar signals is proposed, in which according to the pulsar signal model at the solar system Barycenter（SSB） and the trajectory information of the spacecraft, the real-time photon arrival rate function at the spacecraft is established, then based on this, a scale transforming method is employed to directly generate the photon event time stamps at the spacecraft which follow a non-homogeneous Poisson process. The proposed simulation method takes into account the pulsar spin down law and the influences of the largescale time-space effects introduced in the process of dynamic detection, and thus avoids the complicated iteration procedure involved in the state of the art simulation methods. Finally, a series of simulations are designed to evaluate the performance of the proposed simulation method. The main results can be concluded as follows： 1） The simulated photon event timestamps have a slowly changing period, which are consistent with the pulsar spin down law. 2） The observed pulsar profile accurately reflects how the radiation intensity of pulsars changes over time within a phase cycle, and it has a Pearson correlation coefficient of up to 0.99 with a standard profile. 3） The simulated average fluxes of the pulsars are very close to the true values, and thereby verifies the correctness of the proposed simulation method from an overall point of view. 4） The simulated photon series are very similar to the real data detected by the RXTE explorer, and when the simulation time is longer than 50 s, the relevancy between the simulated profile and the profile obtained from the real data is higher than 0.9. 5） The computational cost of the scale transforming method is much less than that for the commonly used Poisson sifting method and the inverse mapping method. The above results show the validity and high efficiency of the proposed method in terms of the period property, the profile and flux accuracy, the similarity to the RXTE real data and the computational cost.