综合脉冲星时研究进展

Review on research progress of ensemble pulsar time-scale

脉冲星计时分析方法包括广义最小二乘法和贝叶斯方法。在分别介绍这2种分析方法的基础上,概括描述综合脉冲星时算法与研究结果。目前,已经建立并在研究工作中实际采用的综合脉冲星时(EPT)算法,主要包括基于TEMPO2软件包的广义最小二乘算法(频率分析法)、贝叶斯算法和维纳滤波算法。给出了采用不同算法的具有代表性的综合脉冲星时研究结果。基于国际脉冲星计时阵(IPTA)长期计时观测资料,综合脉冲星时研究结果表明,以国际原子时(TAI)为参考,采用不同算法得到的综合脉冲星时EPT-TAI,都能够检测到TAI的系统误差TT-TAI。以地球时(TT)为参考还可以得到综合脉冲星时EPT-TT。以所提出的改进维纳滤波算法得到的综合脉冲星时EPT-TAI为例,其频率稳定度分析表明,综合脉冲星时EPT-TAI基本不存在红噪声,在8年以上的频率稳定度略优于原子时TT-TAI。而综合脉冲星时EPT-TT频率稳定度略优于EPT-TAI。与综合脉冲星时不同,消除二次项的原子时TT-TAI的频率稳定度存在明显低频红噪声。最后,总结3种综合脉冲星时算法的各自特征,讨论关于改进综合脉冲星时短期频率稳定度等问题,并给出脉冲星时研究的有关初步结论。

Now generalized least square fitting and a Bayesian approach to pulsar timing analysis are successfully used.An introduction on these two methods for pulsar timing analysis is provided.Up to today,three kinds of algorithms of constructing an ensemble pulsar time-scale using millisecond pulsar timing data were developed,which were the generalized least square fitting algorithm,the Bayesian analysis technology and the optimal Wiener filtration.We describe the above three algorithms in some details,and show some derived representative results on Ensemble Pulsar Time-scale(EPT)already published and results that we recently derived using improved Wiener filtration from International Pulsar Timing Array(IPTA)data release 2.All the results showed here indicate that the EPT with respect to the International Atomic Time scale(TAI)detected correctly the systematic errors in the TAI.Frequency stability analysis for the ensemble pulsar time-scale EPT-TAI we developed,as an example,indicates that the frequency stability on 8 year and longer time intervals show a little better secular stability than the TT-TAI.The TT-TAI is difference between Terrestrial Time scale(TT)and TAI.Quadratic term in the TT-TAI is removed to make a comparison with pulsar time-scale.Based on the frequency stability analysis,It is clear that TT-TAI shows some red noise,while there is no red noise detected in the EPT-TAI.Finally,we summarize the three algorithms on constructing an ensemble pulsar time scale.The question on improving short time interval stability of pulsar time-scale is discussed.Some preliminary conclusions on EPT research work are given.