High-precision time transfer plays an important role in the areas of fundamental research and applications. Accompanying w ith the remarkable improvements in the ability of generating and measuring high-accuracy time-...High-precision time transfer plays an important role in the areas of fundamental research and applications. Accompanying w ith the remarkable improvements in the ability of generating and measuring high-accuracy time-frequency signal,seeking for new time-transfer techniques betw een distant clocks w ith much further improved accuracy attracts attentions w orld-w idely. The time-transfer technique based on optical pulses has the highest precision presently,and the further improvement in the accuracy is heavily dependent on the time-domain properties of the pulse as w ell as the sensitivity of the applied measurement on the exchanged pulse. The application of optical frequency comb in time transfer for a precision up to femtosecond level are currently the focus of much interest,and has recently achieved many breakthroughs. Further investigations show that,utilizing quantum techniques,i.e. quantum measurement technique and quantum optical pulse source,can lead to a new limit on the measured timing information. Furthermore,it can be immune from atmospheric parameters,such as pressure,temperature,humidity and so on.Such quantum improvements on time-transfer have a bright prospect in the future applications requiring extremely high-accuracy timing and ranging. The potential achievements w ill form a technical basis for the future realization of sub-femtosecond time transfer system.展开更多
Pulsars are very stable spinning stars, which have the potential to application in the work of time-keeping and autonomous navigation in deep space. For time application, an individual pulsar can be regarded as a cloc...Pulsars are very stable spinning stars, which have the potential to application in the work of time-keeping and autonomous navigation in deep space. For time application, an individual pulsar can be regarded as a clock. The accuracy and stability of a pulsar clock are mainly determined by various timing noises and the measurement errors;however, they would be affected by the concrete observational strategy.Taking four millisecond pulsars from the first data released by International Pulsar Timing Array(IPTA) as an example, we investigated the influences of different observational strategies on the properties of pulsar clocks by removing some data in various ways. We find that the long-term stabilities of pulsar clocks are nearly not affected by increasing the observational cadence with a fixed time span. It is also found that the capabilities of prediction by pulsar clocks are also hardly affected by different observational strategies,which is reflected by both the stable weighted root-mean-square(wrms) and the stability of the resulting pre-fit timing residuals, unless the data span is too short or the data period is too far from the start of prediction.展开更多
The distribution probability of the photon interarrival time （PIT） without signal initial phases is derived based on the Poisson model of X-ray pulsar signals, and a pulsar signal detection algorithm employing the P...The distribution probability of the photon interarrival time （PIT） without signal initial phases is derived based on the Poisson model of X-ray pulsar signals, and a pulsar signal detection algorithm employing the PIT sequence is put forward. The joint probability of the PIT sequence is regarded as a function of the distribution probability and used to compare a constant radiation intensity model with the nonhomogeneous Poisson model for the signal detection. The relationship between the number of detected photons and the probabilities of false negative and positive is studied, and the success rate and mean detection time are estimated based on the number of the given photons. For the spacecraft velocity data detection, the changes of time of photon arrival （TOPA） and PIT caused by spacecraft motion are presented first, then the influences on detection are analyzed respectively. By using the analytical pulse profile of PSR B0531＋21, the simulation of the Xray pulsar signal detection is implemented. The simulation results verify the effectiveness of the proposed method, and the contrast tests show that the proposed method is suitable for the spacecraft velocity data detection.展开更多
The detection of gravitational waves(GWs)by pulsar timing arrays(PTAs)is not only a very important supplementation of the verification of general relativity but also a new window to study the evolution of supermassive...The detection of gravitational waves(GWs)by pulsar timing arrays(PTAs)is not only a very important supplementation of the verification of general relativity but also a new window to study the evolution of supermassive binary black holes and the early universe.However,so far the detection sensitivity of PTAs is not good enough to catch signals of GWs due to the disturbance of various noises.In this paper we explore the influences of the correlated noises caused by the reference clock errors and solar system ephemeris errors in pulsar timing on the detection of stochastic gravitational waves background(GWB).We demonstrate the power-law integrated sensitivity curves of GWB detection under the impacts from these correlated noises.From the simulated data,we find that the influence of different reference timescale is non-negligible,and the influence is even quite huge if one uses a very old version of solar system ephemeris.However,the impact from these correlated noises on the sensitivity curve is very limited for the real observational data released by international pulsar timing arrays(IPTA).We also calculate the signalto-noise ratios based on the theoretical GW amplitude permitted by observations.Moreover,we study how the detection sensitivity increases with more pulsar number and longer observation.展开更多
Prior to achieving high precision navigation of a spacecraft using X-ray observations, a pulsar rotation model must be built and analysis of the precise posi- tion of the Earth should be performed using ground pulsar ...Prior to achieving high precision navigation of a spacecraft using X-ray observations, a pulsar rotation model must be built and analysis of the precise posi- tion of the Earth should be performed using ground pulsar timing observations. We can simulate time-of-arrival ground observation data close to actual observed values before using pulsar timing observation data. Considering the correlation between the Earth＇s position and its short arc section of an orbit, we use polynomial regression to build the correlation. Regression coefficients can be calculated using the least square method, and a coordinate component series can also be obtained; that is, we can calcu- late Earth＇s position in the Barycentric Celestial Reference System according to pulse arrival time data and a precise pulsar rotation model. In order to set appropriate param- eters before the actual timing observations for Earth positioning, we can calculate the influence of the spatial distribution of pulsars on errors in the positioning result and the influence of error source variation on positioning by simulation. It is significant that the threshold values of the observation and systematic errors can be established before an actual observation occurs; namely, we can determine the observation mode with small errors and reject the observed data with big errors, thus improving the positioning result.展开更多
The recent stochastic signal observed jointly by NANOGrav,parkes pulsar timing array,European pulsar timing array,and Chinese pulsar timing array can be accounted for by scalarinduced gravitational waves(SIGWs).The so...The recent stochastic signal observed jointly by NANOGrav,parkes pulsar timing array,European pulsar timing array,and Chinese pulsar timing array can be accounted for by scalarinduced gravitational waves(SIGWs).The source of the SIGWs is from the primordial curvature perturbations,and the main contribution to the SIGWs is from the peak of the primordial curvature power spectrum.To effectively model this peak,we apply the Taylor expansion to parameterize it.With the Taylor expansion parameterization,we apply Bayesian methods to constrain the primordial curvature power spectrum based on the NANOGrav 15 year data set.The constraint on the primordial curvature power spectrum possesses a degree of generality,as the Taylor expansion can effectively approximate a wide range of function profiles.展开更多
In pulsar timing, timing residuals are the differences between the observed times of arrival and predictions from the timing model. A comprehensive timing model will produce featureless resid- uals, which are presumab...In pulsar timing, timing residuals are the differences between the observed times of arrival and predictions from the timing model. A comprehensive timing model will produce featureless resid- uals, which are presumably composed of dominating noise and weak physical effects excluded from the timing model （e.g. gravitational waves）. In order to apply optimal statistical methods for detecting weak gravitational wave signals, we need to know the statistical properties of noise components in the residuals. In this paper we utilize a variety of non-parametric statistical tests to analyze the whiteness and Gaussianity of the North American Nanohertz Observatory for Gravitational Waves （NANOGrav） 5- year timing data, which are obtained from Arecibo Observatory and Green Bank Telescope from 2005 to 2010. We find that most of the data are consistent with white noise; many data deviate from Gaussianity at different levels, nevertheless, removing outliers in some pulsars will mitigate the deviations.展开更多
The grazing incidence focusing X-ray pulsar telescope(iFXPT), as the main payload of the X-ray Pulsar Navigation Test Satellite(XPNAV-1), will have great significance on China's space scientific exploration and X-...The grazing incidence focusing X-ray pulsar telescope(iFXPT), as the main payload of the X-ray Pulsar Navigation Test Satellite(XPNAV-1), will have great significance on China's space scientific exploration and X-ray pulsar navigation. With PSR B0531+21(Crab Pulsar) as the observation target, the pulsar profile has been recovered based on the data obtained by iFXPT, realizing the main objective of "observing" PSR B0531+21 for the first time in China. This payload mainly consists of the Wolter-I X-ray optics, silicon drift detector, magnetic deflector, electronics, high-energy particle shield and high-stability structures. Currently, the iFXPT, with its good in-orbit performance, has obtained a considerable observation data. The effective area, sensitivity and energy response have been calibrated both on ground and in-orbit, demonstrating a high degree of consistency. Meanwhile, the in-orbit observation data and information for pulsar navigation has also been analyzed simultaneously. As a result, the feasibility of the exploration scheme and the performance of the telescope have been fully validated.展开更多
脉冲星钟模型保持方法和脉冲星时自主保持精度是决定脉冲星时应用精度的关键。根据地球时TT发布的特点以及脉冲星自转稳定特点,提出基于滑动累积窗口的脉冲星钟模型保持方法。首先利用IPTA第2批发布的2颗脉冲星观测数据开展钟模型保持...脉冲星钟模型保持方法和脉冲星时自主保持精度是决定脉冲星时应用精度的关键。根据地球时TT发布的特点以及脉冲星自转稳定特点,提出基于滑动累积窗口的脉冲星钟模型保持方法。首先利用IPTA第2批发布的2颗脉冲星观测数据开展钟模型保持精度分析,在13年以上的时间窗口内2颗源的自转频率测量值相对于平均值波动幅度在10^(-13)Hz之内,且随着时间窗口累积增加钟参数测量精度单调提高;其次,利用观测数据分析钟模型在滑动预报下的脉冲星时自主保持精度和稳定度,J0437-4715在13.58年内自主保持的脉冲星时与TT(BIPM15)偏差的RMS(root mean square)为0.454μs,长期(13.58年)稳定度为1.77×10^(-15),J1713+0747在17.46年内保持的脉冲星时与TT(BIPM15)偏差为2.471μs,长期(17.46年)稳定度为6.62×10^(-17),相对于最佳保持脉冲星时的精度分别降低24%和0.16%,但提升了短期(<1年)稳定度,长期稳定度略有恶化。展开更多
原子时具有较高的短期稳定度,基于毫秒脉冲星自转建立的脉冲星时具有较高的长期稳定度,两者融合可构建长短稳优势兼具的时间尺度。本文通过经典加权平均算法,初步构建一个脉冲星与原子钟融合的联合时间尺度(composite time scale,CT)。...原子时具有较高的短期稳定度,基于毫秒脉冲星自转建立的脉冲星时具有较高的长期稳定度,两者融合可构建长短稳优势兼具的时间尺度。本文通过经典加权平均算法,初步构建一个脉冲星与原子钟融合的联合时间尺度(composite time scale,CT)。基于国际权度局(BIPM)公布的TA(NTSC)-TAI原子时数据,并选取国际脉冲星计时阵(IPTA)公布的计时精度最高的4颗脉冲星,通过并列加权法和分类加权法这两种组合方式得到CT。结果表明并列加权法得到的CT相对于各脉冲星时在10年以内的稳定度改善明显,4~10年内稳定度与稳定度较高的脉冲星J0437-4715接近。分类加权法得到的CT对比并列加权的稳定度结果在采样区间两极优势明显,0.26年达到5.1×10^(-15),16.8年达到1.0×10^(-15),其中4颗星相比2颗星得到的CT于5.2年后稳定度有显著提高,且分类加权法得到的CT相对于TAI偏差更小,时间尺度更平稳。综上说明原子钟组的短稳特性可以对脉冲星钟组的短期噪声进行抑制,同时脉冲星时可提高联合时间尺度CT的长期稳定度。展开更多
对于脉冲星试验01星的两年实测数据,针对蟹状星云脉冲星星历经历了多次更新的特点,提出了更新标准脉冲轮廓进行X射线计时的改进方法。以一系列观测时长为实测数据分组,再采用改进后的方法进行计时分析并与改进前的结果进行对比。通过对...对于脉冲星试验01星的两年实测数据,针对蟹状星云脉冲星星历经历了多次更新的特点,提出了更新标准脉冲轮廓进行X射线计时的改进方法。以一系列观测时长为实测数据分组,再采用改进后的方法进行计时分析并与改进前的结果进行对比。通过对比改进前后的计时结果,发现改进方法得到的计时残差的均方根(root mean square, RMS)平均降低了14.2%,定位精度平均提高了14.4%,估计原子钟相对频率偏差的精度平均提高了26.2%,体现了改进方法处理经历多次星历更新的Crab脉冲星观测数据的合理性和优越性。此外,改进方法对脉冲星试验01星两年观测数据的稳定度σ_(z)没有量级上的改进,说明改进方法对Crab脉冲星时间稳定度的影响不大。展开更多
氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟...氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟的频率驾驭,并对实时信号加以控制.首先分析了国际脉冲星计时阵(International Pulsar Timing Array,IPTA)第二批发布数据中四颗毫秒脉冲星的稳定度随时间的变化,同时采用哈达玛方差分析了中国科学院国家授时中心(National Time Service Center,NTSC)一台氢钟的频率稳定性能,最终给出了利用脉冲星驾驭氢原子钟频率的方法.展开更多
文摘High-precision time transfer plays an important role in the areas of fundamental research and applications. Accompanying w ith the remarkable improvements in the ability of generating and measuring high-accuracy time-frequency signal,seeking for new time-transfer techniques betw een distant clocks w ith much further improved accuracy attracts attentions w orld-w idely. The time-transfer technique based on optical pulses has the highest precision presently,and the further improvement in the accuracy is heavily dependent on the time-domain properties of the pulse as w ell as the sensitivity of the applied measurement on the exchanged pulse. The application of optical frequency comb in time transfer for a precision up to femtosecond level are currently the focus of much interest,and has recently achieved many breakthroughs. Further investigations show that,utilizing quantum techniques,i.e. quantum measurement technique and quantum optical pulse source,can lead to a new limit on the measured timing information. Furthermore,it can be immune from atmospheric parameters,such as pressure,temperature,humidity and so on.Such quantum improvements on time-transfer have a bright prospect in the future applications requiring extremely high-accuracy timing and ranging. The potential achievements w ill form a technical basis for the future realization of sub-femtosecond time transfer system.
基金supported by the National Natural Science Foundation of China(Grant Nos.U1831130 and U1531112)the program of Youth Innovation Promotion Association CAS(2017450)。
文摘Pulsars are very stable spinning stars, which have the potential to application in the work of time-keeping and autonomous navigation in deep space. For time application, an individual pulsar can be regarded as a clock. The accuracy and stability of a pulsar clock are mainly determined by various timing noises and the measurement errors;however, they would be affected by the concrete observational strategy.Taking four millisecond pulsars from the first data released by International Pulsar Timing Array(IPTA) as an example, we investigated the influences of different observational strategies on the properties of pulsar clocks by removing some data in various ways. We find that the long-term stabilities of pulsar clocks are nearly not affected by increasing the observational cadence with a fixed time span. It is also found that the capabilities of prediction by pulsar clocks are also hardly affected by different observational strategies,which is reflected by both the stable weighted root-mean-square(wrms) and the stability of the resulting pre-fit timing residuals, unless the data span is too short or the data period is too far from the start of prediction.
基金supported by the National Natural Science Foundation of China (61172138)the Open Fund of Key Laboratory of Precision Navigation and Technology,National Time Service Center,CAS (2012PNTT02)
文摘The distribution probability of the photon interarrival time （PIT） without signal initial phases is derived based on the Poisson model of X-ray pulsar signals, and a pulsar signal detection algorithm employing the PIT sequence is put forward. The joint probability of the PIT sequence is regarded as a function of the distribution probability and used to compare a constant radiation intensity model with the nonhomogeneous Poisson model for the signal detection. The relationship between the number of detected photons and the probabilities of false negative and positive is studied, and the success rate and mean detection time are estimated based on the number of the given photons. For the spacecraft velocity data detection, the changes of time of photon arrival （TOPA） and PIT caused by spacecraft motion are presented first, then the influences on detection are analyzed respectively. By using the analytical pulse profile of PSR B0531＋21, the simulation of the Xray pulsar signal detection is implemented. The simulation results verify the effectiveness of the proposed method, and the contrast tests show that the proposed method is suitable for the spacecraft velocity data detection.
基金the National Natural Science Foundation of China(Grant Nos.U1831130 and U1531112)the program of Youth Innovation Promotion Association CAS(2017450)。
文摘The detection of gravitational waves(GWs)by pulsar timing arrays(PTAs)is not only a very important supplementation of the verification of general relativity but also a new window to study the evolution of supermassive binary black holes and the early universe.However,so far the detection sensitivity of PTAs is not good enough to catch signals of GWs due to the disturbance of various noises.In this paper we explore the influences of the correlated noises caused by the reference clock errors and solar system ephemeris errors in pulsar timing on the detection of stochastic gravitational waves background(GWB).We demonstrate the power-law integrated sensitivity curves of GWB detection under the impacts from these correlated noises.From the simulated data,we find that the influence of different reference timescale is non-negligible,and the influence is even quite huge if one uses a very old version of solar system ephemeris.However,the impact from these correlated noises on the sensitivity curve is very limited for the real observational data released by international pulsar timing arrays(IPTA).We also calculate the signalto-noise ratios based on the theoretical GW amplitude permitted by observations.Moreover,we study how the detection sensitivity increases with more pulsar number and longer observation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10973030,10973032,11003039,10903032 and 10973049)the National Science Foundation of Shanghai,China (Grant No. 10ZR1435700)
文摘Prior to achieving high precision navigation of a spacecraft using X-ray observations, a pulsar rotation model must be built and analysis of the precise posi- tion of the Earth should be performed using ground pulsar timing observations. We can simulate time-of-arrival ground observation data close to actual observed values before using pulsar timing observation data. Considering the correlation between the Earth＇s position and its short arc section of an orbit, we use polynomial regression to build the correlation. Regression coefficients can be calculated using the least square method, and a coordinate component series can also be obtained; that is, we can calcu- late Earth＇s position in the Barycentric Celestial Reference System according to pulse arrival time data and a precise pulsar rotation model. In order to set appropriate param- eters before the actual timing observations for Earth positioning, we can calculate the influence of the spatial distribution of pulsars on errors in the positioning result and the influence of error source variation on positioning by simulation. It is significant that the threshold values of the observation and systematic errors can be established before an actual observation occurs; namely, we can determine the observation mode with small errors and reject the observed data with big errors, thus improving the positioning result.
基金supported in part by the National Natural Science Foundation of China under Grant No.12305060the Talent-Introduction Program of Hubei Polytechnic University under Grant No.19xjk25R。
文摘The recent stochastic signal observed jointly by NANOGrav,parkes pulsar timing array,European pulsar timing array,and Chinese pulsar timing array can be accounted for by scalarinduced gravitational waves(SIGWs).The source of the SIGWs is from the primordial curvature perturbations,and the main contribution to the SIGWs is from the peak of the primordial curvature power spectrum.To effectively model this peak,we apply the Taylor expansion to parameterize it.With the Taylor expansion parameterization,we apply Bayesian methods to constrain the primordial curvature power spectrum based on the NANOGrav 15 year data set.The constraint on the primordial curvature power spectrum possesses a degree of generality,as the Taylor expansion can effectively approximate a wide range of function profiles.
基金supported by the National Science Foundation(NSF)under PIRE grant0968296support by the National Natural Science Foundation of China(Grant Nos.11503007,91636111 and 11690021)+2 种基金partial support through the New York Space Grant Consortiumsupport by NASA through the Einstein Fellowship grant PF4-150120upport from the JPL RTD program
文摘In pulsar timing, timing residuals are the differences between the observed times of arrival and predictions from the timing model. A comprehensive timing model will produce featureless resid- uals, which are presumably composed of dominating noise and weak physical effects excluded from the timing model （e.g. gravitational waves）. In order to apply optimal statistical methods for detecting weak gravitational wave signals, we need to know the statistical properties of noise components in the residuals. In this paper we utilize a variety of non-parametric statistical tests to analyze the whiteness and Gaussianity of the North American Nanohertz Observatory for Gravitational Waves （NANOGrav） 5- year timing data, which are obtained from Arecibo Observatory and Green Bank Telescope from 2005 to 2010. We find that most of the data are consistent with white noise; many data deviate from Gaussianity at different levels, nevertheless, removing outliers in some pulsars will mitigate the deviations.
文摘The grazing incidence focusing X-ray pulsar telescope(iFXPT), as the main payload of the X-ray Pulsar Navigation Test Satellite(XPNAV-1), will have great significance on China's space scientific exploration and X-ray pulsar navigation. With PSR B0531+21(Crab Pulsar) as the observation target, the pulsar profile has been recovered based on the data obtained by iFXPT, realizing the main objective of "observing" PSR B0531+21 for the first time in China. This payload mainly consists of the Wolter-I X-ray optics, silicon drift detector, magnetic deflector, electronics, high-energy particle shield and high-stability structures. Currently, the iFXPT, with its good in-orbit performance, has obtained a considerable observation data. The effective area, sensitivity and energy response have been calibrated both on ground and in-orbit, demonstrating a high degree of consistency. Meanwhile, the in-orbit observation data and information for pulsar navigation has also been analyzed simultaneously. As a result, the feasibility of the exploration scheme and the performance of the telescope have been fully validated.
文摘脉冲星钟模型保持方法和脉冲星时自主保持精度是决定脉冲星时应用精度的关键。根据地球时TT发布的特点以及脉冲星自转稳定特点,提出基于滑动累积窗口的脉冲星钟模型保持方法。首先利用IPTA第2批发布的2颗脉冲星观测数据开展钟模型保持精度分析,在13年以上的时间窗口内2颗源的自转频率测量值相对于平均值波动幅度在10^(-13)Hz之内,且随着时间窗口累积增加钟参数测量精度单调提高;其次,利用观测数据分析钟模型在滑动预报下的脉冲星时自主保持精度和稳定度,J0437-4715在13.58年内自主保持的脉冲星时与TT(BIPM15)偏差的RMS(root mean square)为0.454μs,长期(13.58年)稳定度为1.77×10^(-15),J1713+0747在17.46年内保持的脉冲星时与TT(BIPM15)偏差为2.471μs,长期(17.46年)稳定度为6.62×10^(-17),相对于最佳保持脉冲星时的精度分别降低24%和0.16%,但提升了短期(<1年)稳定度,长期稳定度略有恶化。
文摘原子时具有较高的短期稳定度,基于毫秒脉冲星自转建立的脉冲星时具有较高的长期稳定度,两者融合可构建长短稳优势兼具的时间尺度。本文通过经典加权平均算法,初步构建一个脉冲星与原子钟融合的联合时间尺度(composite time scale,CT)。基于国际权度局(BIPM)公布的TA(NTSC)-TAI原子时数据,并选取国际脉冲星计时阵(IPTA)公布的计时精度最高的4颗脉冲星,通过并列加权法和分类加权法这两种组合方式得到CT。结果表明并列加权法得到的CT相对于各脉冲星时在10年以内的稳定度改善明显,4~10年内稳定度与稳定度较高的脉冲星J0437-4715接近。分类加权法得到的CT对比并列加权的稳定度结果在采样区间两极优势明显,0.26年达到5.1×10^(-15),16.8年达到1.0×10^(-15),其中4颗星相比2颗星得到的CT于5.2年后稳定度有显著提高,且分类加权法得到的CT相对于TAI偏差更小,时间尺度更平稳。综上说明原子钟组的短稳特性可以对脉冲星钟组的短期噪声进行抑制,同时脉冲星时可提高联合时间尺度CT的长期稳定度。
文摘对于脉冲星试验01星的两年实测数据,针对蟹状星云脉冲星星历经历了多次更新的特点,提出了更新标准脉冲轮廓进行X射线计时的改进方法。以一系列观测时长为实测数据分组,再采用改进后的方法进行计时分析并与改进前的结果进行对比。通过对比改进前后的计时结果,发现改进方法得到的计时残差的均方根(root mean square, RMS)平均降低了14.2%,定位精度平均提高了14.4%,估计原子钟相对频率偏差的精度平均提高了26.2%,体现了改进方法处理经历多次星历更新的Crab脉冲星观测数据的合理性和优越性。此外,改进方法对脉冲星试验01星两年观测数据的稳定度σ_(z)没有量级上的改进,说明改进方法对Crab脉冲星时间稳定度的影响不大。
文摘氢原子钟具有较高的短期稳定度,将其作为主钟可在短期内产生高精度的本地时间信号.但氢钟存在频率漂移现象,导致其长期稳定度较差,从而影响本地时间的准确性.毫秒脉冲星自转高度稳定,借助于其长期稳定度高的特性,可定期实现对氢原子钟的频率驾驭,并对实时信号加以控制.首先分析了国际脉冲星计时阵(International Pulsar Timing Array,IPTA)第二批发布数据中四颗毫秒脉冲星的稳定度随时间的变化,同时采用哈达玛方差分析了中国科学院国家授时中心(National Time Service Center,NTSC)一台氢钟的频率稳定性能,最终给出了利用脉冲星驾驭氢原子钟频率的方法.
文摘通过对比NICER(Neutron Star Interior Composition Explorer)和XPNAV-1(X-ray Pulsar Navigation-1)关于Crab脉冲星同一时段(108天)观测数据的计时处理结果,发现在周期跃变发生前的时段(95天),NICER数据的拟合前计时残差的RMS(root mean square)为5.77μs,远优于XPNAV-1数据的拟合前计时残差的RMS 51.56μs,体现了NICER在有效面积、探测效率、数据采集等方面的优势,给未来我国的X射线脉冲星探测器研制提供了发展方向;而在周期跃变发生后的时段(13天),发现XPNAV-1数据的拟合前计时残差的RMS为55.87μs,而NICER数据的拟合前计时残差的RMS为167.27μs,周期跃变对NICER的影响更大,说明在处理周期跃变发生后时段的NICER数据时,由于NICER的观测精度非常高,需要更频繁地更新Crab星历。最后分别得到了两个探测器整段数据的计时残差。XPNAV-1数据的拟合前计时残差的RMS为55.94μs,而NICER数据的拟合前计时残差的RMS为64.34μs,这说明NICER数据受周期跃变影响更为明显,进一步证明了上述结论。
