Pulsar detection has become an active research topic in radio astronomy recently.One of the essential procedures for pulsar detection is pulsar candidate sifting(PCS),a procedure for identifying potential pulsar signa...Pulsar detection has become an active research topic in radio astronomy recently.One of the essential procedures for pulsar detection is pulsar candidate sifting(PCS),a procedure for identifying potential pulsar signals in a survey.However,pulsar candidates are always class-imbalanced,as most candidates are non-pulsars such as RFI and only a tiny part of them are from real pulsars.Class imbalance can greatly affect the performance of machine learning(ML)models,resulting in a heavy cost as some real pulsars are misjudged.To deal with the problem,techniques of choosing relevant features to discriminate pulsars from non-pulsars are focused on,which is known as feature selection.Feature selection is a process of selecting a subset of the most relevant features from a feature pool.The distinguishing features between pulsars and non-pulsars can significantly improve the performance of the classifier even if the data are highly imbalanced.In this work,an algorithm for feature selection called the K-fold Relief-Greedy(KFRG)algorithm is designed.KFRG is a two-stage algorithm.In the first stage,it filters out some irrelevant features according to their K-fold Relief scores,while in the second stage,it removes the redundant features and selects the most relevant features by a forward greedy search strategy.Experiments on the data set of the High Time Resolution Universe survey verified that ML models based on KFRG are capable of PCS,correctly separating pulsars from non-pulsars even if the candidates are highly class-imbalanced.展开更多
Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s positio...Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s position is arcminutes off from its true position.Such a position error leads to significant arrival time shifts as a result of the Earth’s orbital motion.Traditional down-hill fitting timing algorithms become ineffective when our model predicts the wrong pulse rotations for our next observation.For some pulsars whose model prediction is not too far off,the correct rotation number could be found by trial-and-error methods.For the remaining challenging pulsars,a more generalized method is called for.This paper proposes a GPU-based algorithm that could exhaustively search a large area of trail positions for probable timing solutions.This could help find phase-connected timing solutions for new pulsars using brute force.展开更多
For high-precision pulsar timing analysis and low-frequency gravitational wave detection,it is essential to accurately determine pulsar pulse times of arrival(ToAs)and associated uncertainties.To measure the ToAs and ...For high-precision pulsar timing analysis and low-frequency gravitational wave detection,it is essential to accurately determine pulsar pulse times of arrival(ToAs)and associated uncertainties.To measure the ToAs and their uncertainties,various cross-correlation-based techniques can be employed.We develop methodologies to investigate the impact of the template-matching method,profile shape,signal-to-noise ratio of both template and observation on ToA uncertainties.These methodologies are then applied to data from the International Pulsar Timing Array.We demonstrate that the Fourier domain Markov chain Monte Carlo method is generally superior to other methods,while the Gaussian interpolation shift method outperforms other methods in certain cases,such as profiles with large duty cycles or smooth profiles without sharp features.However,it is important to note that our study focuses solely on ToA uncertainty,and the optimal method for determining both ToA and ToA uncertainty may differ.展开更多
The increasing radio frequency interference(RFI)is a well-recognized problem in radio astronomy research.Pulsars and Fast Radio Bursts(FRBs)are high-priority science targets of the ongoing Commercial Radio Astronomy F...The increasing radio frequency interference(RFI)is a well-recognized problem in radio astronomy research.Pulsars and Fast Radio Bursts(FRBs)are high-priority science targets of the ongoing Commercial Radio Astronomy FAST Survey(CRAFTS).To improve the quality of RFI removal in searches of pulsars and FRBs based on CRAFTS multi-beam data,we here propose an intuitive but powerful RFI mitigation pipeline(CCF-ST).The“CCF-ST”is a spatial filter constructed by signal cross-correlation function(CCF)and Sum-Threshold(ST)algorithm.The RFI marking result is saved in a“mask”file,a binary format for RFI masks in PRESTO.Three known pulsars,PSR B0525-21,PSR B0621-04,and PSR J0943+2252 from CRAFTS L-band 19 beams data are used for evaluation of the performance of CCF-ST in comparison with other methods,such as PRESTO’s“rfifind”,ArPLS-ST and ArPLS-SF.The result shows that CCF-ST can reduce effective data loss rate and improves the detected signal-to-noise ratio of the pulsations by~26%and~18%respectively compared with PRESTO’s“rfifind”and ArPLS-ST.The CCF-ST also has the advantage of low computational cost,e.g.,reducing the time consumption by~40%and memory consumption by~90%compared with ArPLS-SF.We expect that the new RFI mitigation and analysis toolkit(CCF-ST)demonstrated in this paper can be applied to CRAFTS and other multi-beam telescope observations to improve the data quality and efficiency of pulsar and FRB searches.展开更多
A digital pulsar backend based on a Field Programmable Gate Array （FPGA） is developed. It is designed for incoherent de-dispersion of pulsar observations and has a maximum bandwidth of 512MHz. The channel bandwidth ...A digital pulsar backend based on a Field Programmable Gate Array （FPGA） is developed. It is designed for incoherent de-dispersion of pulsar observations and has a maximum bandwidth of 512MHz. The channel bandwidth is fixed to 1 MHz, and the highest time resolution is 10 p.s. Testing observations were carried out using the Urumqi 25-m telescope administered by Xinjiang Astronomical Observatory and the Kunming 40-m telescope administered by Yunnan Observatories, targeting PSR J0332＋5434 in the L band and PSR J0437-4715 in the S band, respectively. The successful observation of PSR J0437-4715 demonstrates its ability to observe millisecond pulsars.展开更多
Based on dividing the profile into a number of absolute phase intervals, the phaseresolved spectra （PHRS） are derived from published time-aligned average profiles at radio frequencies over two decades for the classi...Based on dividing the profile into a number of absolute phase intervals, the phaseresolved spectra （PHRS） are derived from published time-aligned average profiles at radio frequencies over two decades for the classic conal-double pulsar B1133＋16. The relative spectral index, defined as the difference between the spectral indices of a reference and the given arbitrary phase interval, is obtained by power-law fit at each phase interval. The derived phase-resolved spectra show an ＂M-like＂ shape, of which the leading part and trailing part are approximately symmetrical. The basic feature of the PHRS is that the spectrum first flattens then steepens as the pulse phase sweeps from the profile center to the profile edges. The PHRS provide a coherent explanation of the major features of profile evolution of B 1133＋ 16, namely, the pulse width shrinkage with increasing frequency and the frequency evolution of the relative intensity between the leading and trailing conal components, and the bridge emission. The PHRS may be an indicator for emission spectral variation across the pulsar magnetosphere. Possible mapping from PHRS to emission-location-dependent spectral variation is presented, and some intrinsic mechanisms are discussed.展开更多
脉冲星在天体演化、物理学、计时、深空自主导航、引力波探测等领域均有重要的学术和应用价值,脉冲星搜寻及其应用也成为了当前天文界热点研究之一。为了更好地探究脉冲星搜寻及其应用领域的研究现状和未来发展趋势,在Web of Science(W...脉冲星在天体演化、物理学、计时、深空自主导航、引力波探测等领域均有重要的学术和应用价值,脉冲星搜寻及其应用也成为了当前天文界热点研究之一。为了更好地探究脉冲星搜寻及其应用领域的研究现状和未来发展趋势,在Web of Science(WOS)数据库筛选出有关脉冲星搜寻及应用的964篇文献,在阅读核心文献的基础上,采用数据分析和可视化方法进行深入探讨。结果表明,脉冲星搜寻及应用领域的研究经历了初始探索阶段和稳健发展阶段,目前进入蓬勃增长阶段。该领域各国之间密切合作,形成了三大主要的研究群体。脉冲星搜寻及其应用研究在未来将产生如直接探测引力波、深空自主导航等重要科研价值和实际应用结果,将进一步丰富和多元化脉冲星的研究领域。展开更多
由于截然不同的物理机制,毫秒脉冲星可产生与原子时尺度完全不同的另一类时间尺度.利用长期的脉冲星计时观测数据可建立综合脉冲星时间尺度,但通常脉冲星计时观测是非等间隔采样,并且有些脉冲星的观测间隔过长等,这些因素均对综合脉冲...由于截然不同的物理机制,毫秒脉冲星可产生与原子时尺度完全不同的另一类时间尺度.利用长期的脉冲星计时观测数据可建立综合脉冲星时间尺度,但通常脉冲星计时观测是非等间隔采样,并且有些脉冲星的观测间隔过长等,这些因素均对综合脉冲星时间尺度的产生造成很大的困难.因此,提出了一种新的算法来计算综合脉冲星时间尺度,即:首先选用三次样条插值方法进行内插,并使观测数据间隔均匀;其次采用Vondrak滤波方法对观测序列进行平滑处理并去除高频噪声;最后再利用加权算法产生综合脉冲星时间尺度.利用NANOGRAV(North American Nanohertz Observatory for Gravitational Waves)最新发布的长达9 yr的观测数据,计算得到了综合脉冲星时间尺度,它的长期稳定度(取样间隔大于1 yr)优于3.4×10^(-15).研究结果表明:这种方法可有效降低脉冲星计时残差中的噪声影响,同时可提高综合脉冲星时间尺度的长期稳定度.展开更多
讨论了X射线脉冲星光子到达的周期平稳Poisson模型和到达时刻(Time of arrival,TOA)估计问题.在此基础上,得到了脉冲到达时刻的最大似然估计和克拉美-罗限(Cramer-Rao boundary,CRB),并推导了低信噪比情况下的似然函数近似表达和克拉美...讨论了X射线脉冲星光子到达的周期平稳Poisson模型和到达时刻(Time of arrival,TOA)估计问题.在此基础上,得到了脉冲到达时刻的最大似然估计和克拉美-罗限(Cramer-Rao boundary,CRB),并推导了低信噪比情况下的似然函数近似表达和克拉美-罗限.利用解析的脉冲轮廓,对PSR B1821-24的TOA估计进行了Monte Carlo仿真,讨论了不同观测时间和信噪比下的估计误差,给出了相应的信噪比门限.研究表明:该分析方法能够有效估计X射线脉冲星的TOA定时精度,有利于评估其在各种应用中的性能.展开更多
基金support from the National Natural Science Foundation of China(NSFC,grant Nos.11973022 and 12373108)the Natural Science Foundation of Guangdong Province(No.2020A1515010710)Hanshan Normal University Startup Foundation for Doctor Scientific Research(No.QD202129)。
文摘Pulsar detection has become an active research topic in radio astronomy recently.One of the essential procedures for pulsar detection is pulsar candidate sifting(PCS),a procedure for identifying potential pulsar signals in a survey.However,pulsar candidates are always class-imbalanced,as most candidates are non-pulsars such as RFI and only a tiny part of them are from real pulsars.Class imbalance can greatly affect the performance of machine learning(ML)models,resulting in a heavy cost as some real pulsars are misjudged.To deal with the problem,techniques of choosing relevant features to discriminate pulsars from non-pulsars are focused on,which is known as feature selection.Feature selection is a process of selecting a subset of the most relevant features from a feature pool.The distinguishing features between pulsars and non-pulsars can significantly improve the performance of the classifier even if the data are highly imbalanced.In this work,an algorithm for feature selection called the K-fold Relief-Greedy(KFRG)algorithm is designed.KFRG is a two-stage algorithm.In the first stage,it filters out some irrelevant features according to their K-fold Relief scores,while in the second stage,it removes the redundant features and selects the most relevant features by a forward greedy search strategy.Experiments on the data set of the High Time Resolution Universe survey verified that ML models based on KFRG are capable of PCS,correctly separating pulsars from non-pulsars even if the candidates are highly class-imbalanced.
基金supported by the National Natural Science Foundation of China(12041303)the National SKA Program of China(2020SKA0120200)+2 种基金the CAS Project for Young Scientists in Basic Research YSBR-063the National Natural Science Foundation of China(NSFC grant Nos.12203070 and Nos.12203072)the CAS-MPG LEGACY project。
文摘Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s position is arcminutes off from its true position.Such a position error leads to significant arrival time shifts as a result of the Earth’s orbital motion.Traditional down-hill fitting timing algorithms become ineffective when our model predicts the wrong pulse rotations for our next observation.For some pulsars whose model prediction is not too far off,the correct rotation number could be found by trial-and-error methods.For the remaining challenging pulsars,a more generalized method is called for.This paper proposes a GPU-based algorithm that could exhaustively search a large area of trail positions for probable timing solutions.This could help find phase-connected timing solutions for new pulsars using brute force.
基金support by the Deutsche Forschungsgemeinschaft(DFG)through the Heisenberg program(Project No.433075039)。
文摘For high-precision pulsar timing analysis and low-frequency gravitational wave detection,it is essential to accurately determine pulsar pulse times of arrival(ToAs)and associated uncertainties.To measure the ToAs and their uncertainties,various cross-correlation-based techniques can be employed.We develop methodologies to investigate the impact of the template-matching method,profile shape,signal-to-noise ratio of both template and observation on ToA uncertainties.These methodologies are then applied to data from the International Pulsar Timing Array.We demonstrate that the Fourier domain Markov chain Monte Carlo method is generally superior to other methods,while the Gaussian interpolation shift method outperforms other methods in certain cases,such as profiles with large duty cycles or smooth profiles without sharp features.However,it is important to note that our study focuses solely on ToA uncertainty,and the optimal method for determining both ToA and ToA uncertainty may differ.
基金supported by National Natural Science Foundation of China(NSFC)under Nos.11988101,U183110134,11703047,11773041,and U1831131support by the Youth Innovation Promotion Association CAS(id.2021055)cultivation project for FAST scientific payoff and research achievement of CAMS-CAS。
文摘The increasing radio frequency interference(RFI)is a well-recognized problem in radio astronomy research.Pulsars and Fast Radio Bursts(FRBs)are high-priority science targets of the ongoing Commercial Radio Astronomy FAST Survey(CRAFTS).To improve the quality of RFI removal in searches of pulsars and FRBs based on CRAFTS multi-beam data,we here propose an intuitive but powerful RFI mitigation pipeline(CCF-ST).The“CCF-ST”is a spatial filter constructed by signal cross-correlation function(CCF)and Sum-Threshold(ST)algorithm.The RFI marking result is saved in a“mask”file,a binary format for RFI masks in PRESTO.Three known pulsars,PSR B0525-21,PSR B0621-04,and PSR J0943+2252 from CRAFTS L-band 19 beams data are used for evaluation of the performance of CCF-ST in comparison with other methods,such as PRESTO’s“rfifind”,ArPLS-ST and ArPLS-SF.The result shows that CCF-ST can reduce effective data loss rate and improves the detected signal-to-noise ratio of the pulsations by~26%and~18%respectively compared with PRESTO’s“rfifind”and ArPLS-ST.The CCF-ST also has the advantage of low computational cost,e.g.,reducing the time consumption by~40%and memory consumption by~90%compared with ArPLS-SF.We expect that the new RFI mitigation and analysis toolkit(CCF-ST)demonstrated in this paper can be applied to CRAFTS and other multi-beam telescope observations to improve the data quality and efficiency of pulsar and FRB searches.
基金supported by the National Natural Science Foundation of China(Grant Nos.10821061 and10833003)
文摘A digital pulsar backend based on a Field Programmable Gate Array （FPGA） is developed. It is designed for incoherent de-dispersion of pulsar observations and has a maximum bandwidth of 512MHz. The channel bandwidth is fixed to 1 MHz, and the highest time resolution is 10 p.s. Testing observations were carried out using the Urumqi 25-m telescope administered by Xinjiang Astronomical Observatory and the Kunming 40-m telescope administered by Yunnan Observatories, targeting PSR J0332＋5434 in the L band and PSR J0437-4715 in the S band, respectively. The successful observation of PSR J0437-4715 demonstrates its ability to observe millisecond pulsars.
基金Supported by the National Natural Science Foundation of China.
文摘Based on dividing the profile into a number of absolute phase intervals, the phaseresolved spectra （PHRS） are derived from published time-aligned average profiles at radio frequencies over two decades for the classic conal-double pulsar B1133＋16. The relative spectral index, defined as the difference between the spectral indices of a reference and the given arbitrary phase interval, is obtained by power-law fit at each phase interval. The derived phase-resolved spectra show an ＂M-like＂ shape, of which the leading part and trailing part are approximately symmetrical. The basic feature of the PHRS is that the spectrum first flattens then steepens as the pulse phase sweeps from the profile center to the profile edges. The PHRS provide a coherent explanation of the major features of profile evolution of B 1133＋ 16, namely, the pulse width shrinkage with increasing frequency and the frequency evolution of the relative intensity between the leading and trailing conal components, and the bridge emission. The PHRS may be an indicator for emission spectral variation across the pulsar magnetosphere. Possible mapping from PHRS to emission-location-dependent spectral variation is presented, and some intrinsic mechanisms are discussed.
文摘脉冲星在天体演化、物理学、计时、深空自主导航、引力波探测等领域均有重要的学术和应用价值,脉冲星搜寻及其应用也成为了当前天文界热点研究之一。为了更好地探究脉冲星搜寻及其应用领域的研究现状和未来发展趋势,在Web of Science(WOS)数据库筛选出有关脉冲星搜寻及应用的964篇文献,在阅读核心文献的基础上,采用数据分析和可视化方法进行深入探讨。结果表明,脉冲星搜寻及应用领域的研究经历了初始探索阶段和稳健发展阶段,目前进入蓬勃增长阶段。该领域各国之间密切合作,形成了三大主要的研究群体。脉冲星搜寻及其应用研究在未来将产生如直接探测引力波、深空自主导航等重要科研价值和实际应用结果,将进一步丰富和多元化脉冲星的研究领域。
文摘由于截然不同的物理机制,毫秒脉冲星可产生与原子时尺度完全不同的另一类时间尺度.利用长期的脉冲星计时观测数据可建立综合脉冲星时间尺度,但通常脉冲星计时观测是非等间隔采样,并且有些脉冲星的观测间隔过长等,这些因素均对综合脉冲星时间尺度的产生造成很大的困难.因此,提出了一种新的算法来计算综合脉冲星时间尺度,即:首先选用三次样条插值方法进行内插,并使观测数据间隔均匀;其次采用Vondrak滤波方法对观测序列进行平滑处理并去除高频噪声;最后再利用加权算法产生综合脉冲星时间尺度.利用NANOGRAV(North American Nanohertz Observatory for Gravitational Waves)最新发布的长达9 yr的观测数据,计算得到了综合脉冲星时间尺度,它的长期稳定度(取样间隔大于1 yr)优于3.4×10^(-15).研究结果表明:这种方法可有效降低脉冲星计时残差中的噪声影响,同时可提高综合脉冲星时间尺度的长期稳定度.
