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Time-resolved Spectral Properties of Fermi-GBM Bright Long Gamma-Ray Bursts

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Research in Astronomy and Astrophysics 2024年第2期24卷 58-73页

作者： Wan-Kai Wang Wei Xie Zhi-Fu Gao Shuo Xiao Ai-Jun Dong Bin Zhang Qi-Jun Zhi Department of Astronomy School of Physics and Electronic ScienceGuizhou Normal UniversityGuiyang 550001China Guizhou Provincial Key Laboratory of Radio Astronomy Data Processing Guizhou Normal UniversityGuiyang 550001China Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China

The prompt emission mechanism of gamma-ray bursts(GRBs)is still unclear,and the time-resolved spectral analysis of GRBs is a powerful tool for studying their underlying physical processes.We performed a detailed time-resolved spectral analysis of 78 bright long GRB samples detected by Fermi/Gamma-ray Burst Monitor.A total of 1490 spectra were obtained and their properties were studied using a typical Band-shape model.First,the parameter distributions of the time-resolved spectrum are given as follows:the low-energy spectral indexα~-0.72,high-energy spectral indexβ~2.42,the peak energy E_(p)~221.69 keV,and the energy flux F~7.49×10^(-6)erg cm^(-2)s^(-1).More than 80%of the bursts exhibit the hardest low-energy spectral indexα_(max),exceeding the synchrotron limit(-2/3).Second,the evolution patterns of a and E_(p)were statistically analyzed.The results show that for multi-pulse GRBs the intensity-tracking pattern is more common than the hard-to-soft pattern in the evolution of both E_(p)andα.The hard-to-soft pattern is generally shown in single-pulse GRBs or in the initial pulse of multi-pulse GRBs.Finally,we found a significant positive correlation between F and E_(p),with half of the samples exhibiting a positive correlation between F andα.We discussed the spectral evolution of different radiation models.The diversity of spectral evolution patterns indicates that there may be more than one radiation mechanism occurring in the GRB radiation process,including photo spheric radiation and synchrotron radiation.However,it may also involve only one radiation mechanism,but more complicated physical details need to be considered.

关键词： (stars:)gamma-ray burst general-methods statistical-methods data analysis

Free Energy of Anisotropic Strangeon Stars

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Research in Astronomy and Astrophysics 2024年第2期24卷 50-57页

作者： Shichuan Chen Yong Gao Enping Zhou Renxin Xu Department of Astronomy School of PhysicsPeking UniversityBeijing 100871China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy School of PhysicsHuazhong University of Science and TechnologyWuhan 430074China

Can pulsar-like compact objects release further huge free energy besides the kinematic energy of rotation?This is actually relevant to the equation of state of cold supra-nuclear matter,which is still under hot debate.Enormous energy is surely needed to understand various observations,such asγ-ray bursts,fast radio bursts and softγ-ray repeaters.In this paper,the elastic/gravitational free energy of solid strangeon stars is revisited for strangeon stars,with two anisotropic models to calculate in general relativity.It is found that huge free energy(>10^(46)erg)could be released via starquakes,given an extremely small anisotropy((p_(t)-p_(r))/p_(r)~10^(-4),with pt/pr the tangential/radial pressure),implying that pulsar-like stars could have great potential of free energy release without extremely strong magnetic fields in the solid strangeon star model.

关键词： (stars:)pulsars general-methods numerical-(stars:)gamma-ray bursts general

Dealing with the Data Imbalance Problem in Pulsar Candidate Sifting Based on Feature Selection

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Research in Astronomy and Astrophysics 2024年第2期24卷 125-137页

作者： Haitao Lin Xiangru Li School of Mathematics and Statistics Hanshan Normal UniversityChaozhou 521000China School of Computer Science South China Normal UniversityGuangzhou 510631China

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.

关键词： methods data analysis-(stars:)pulsars general-methods statistical

A Search Technique Based on Deep Learning for Fast Radio Bursts and Initial Results for FRB 20201124A with the NSRT

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Research in Astronomy and Astrophysics 2022年第10期22卷 77-85页

作者： Yan-Ling Liu Jian Li Zhi-Yong Liu Mao-Zheng Chen Jian-Ping Yuan Na Wang Rai Yuen Hao Yan Xinjiang Astronomical observatory Chinese Academy of SciencesUrumqi 830011China University of Chinese Academy of Sciences Beijing 100049China Key Laboratory of Radio Astronomy Chinese Academy of SciencesNanjing 210033China Xinjiang Key Laboratory of Microwave Technology Urumqi 830011China

The origin and phenomenology of Fast Radio Bursts(FRBs) remain unknown. Fast and efficient search technology for FRBs is critical for triggering immediate multi-wavelength follow-up and voltage data dump. This paper proposes a dispersed dynamic spectra search(DDSS) pipeline for FRB searching based on deep learning, which performs the search directly from observational raw data, rather than relying on generated FRB candidates from single-pulse search algorithms that are based on de-dispersion. We train our deep learning network model using simulated FRBs as positive and negative samples extracted from the observational data of the Nanshan 26 m radio telescope(NSRT)at Xinjiang Astronomical Observatory. The observational data of PSR J1935+1616 are fed into the pipeline to verify the validity and performance of the pipeline. Results of the experiment show that our pipeline can efficiently search single-pulse events with a precision above 99.6%, which satisfies the desired precision for selective voltage data dump. In March 2022, we successfully detected the FRBs emanating from the repeating case of FRB 20201124A with the DDSS pipeline in L-band observations using the NSRT. The DDSS pipeline shows excellent sensitivity in identifying weak single pulses, and its high precision greatly reduces the need for manual review.

关键词： radio continuum general-methods data analysis-methods observational

Fractions of Compact Object Binaries in Star Clusters:Theoretical Predictions

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Research in Astronomy and Astrophysics 2023年第2期23卷 241-248页

作者： Zhong-Mu Li Bhusan Kayastha Albrecht Kamlah Peter Berczik Yang-Yang Deng Rainer Spurzem Institute for Astronomy Dali UniversityDali 671003China National Astronomical Observatories&Key Laboratory of Computational Astrophysics Chinese Academy of Sciences NAOC/CASBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China Zentrum für Astronomie-Astronomisches Rechen-Institut Monchofstr.12-14Heidelberg D-69120Germany Max-Planck-Institut fr Astronomie Konigstuhl 17D-69117 HeidelbergGermany Main Astronomical Observatory National Academy of Sciences of Ukraine27 Akademika Zabolotnoho St03143KyivUkraine Konkoly Observatory Research Centre for Astronomy and Earth SciencesEotvos Loránd Research Network(ELKH)MTA Centre of ExcellenceKonkoly Thege Miklos ut 15-171121 BudapestHungary Yunnan Observatories Chinese Academy of SciencesKunming650216China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China

The binary population in field stars and star clusters contributes to the formation of gravitational wave(GW)sources.However,the fraction of compact-object binaries(CBs),which is an important feature parameter of binary populations,is still difficult to measure and very uncertain.This paper predicts the fractions of important CBs and semi-compact object binaries(SCBs) making use of an advanced stellar population synthesis technique.A comparison with the result of N-body simulation is also presented.It is found that most CBs are formed within about 500 Myr after the starburst.The fractions of CBs and SCBs are demonstrated to correlate with stellar metallicity.The higher the metallicity becomes,the smaller the fraction of black hole binaries(BHBs),neutron star binaries(NSBs) and SCBs.This suggests that the GW sources of BHBs and NSBs are more likely to form in metal-poor environments.However,the fraction of black hole-neutron star binaries is shown to be larger for metalrich populations on average.

关键词： (stars:)binaries visual-gravitational waves-(Galaxy:)globular clusters general-methods numerical

Research on Ultra-wide Bandwidth Low-frequency Signal Channelization for Xinjiang 110m Radio Telescope

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Research in Astronomy and Astrophysics 2023年第12期23卷 263-274页

作者： Hai-Long Zhang Ya-Zhou Zhang Meng Zhang Jie Wang Jian Li Xin-Chen Ye Xin Pei Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China University of Chinese Academy of Sciences Beijing 100049China Key Laboratory of Radio Astronomy Chinese Academy of SciencesNanjing 210008China National Astronomical Data Center Beijing 100101China School of Cyber Science and Engineering Qufu Normal UniversityQufu 273165China

Aiming at the subband division of ultra-wide bandwidth low-frequency(UWL)signal(frequency coverage range:704–4032 MHz)of the Xinjiang 110 m QiTai radio Telescope(QTT),a scheme of ultra-wide bandwidth signal is designed.First,we analyze the effect of different window functions such as the Hanning window,Hamming window,and Kaiser window on the performance of finite impulse response(FIR)digital filters,and implement a critical sampling polyphase filter bank(CS-PFB)based on the Hamming window FIR digital filter.Second,we generate 3328 MHz simulation data of ultra-wideband pulsar baseband in the frequency range of 704–4032 MHz using the ultra-wide bandwidth pulsar baseband data generation algorithm based on the 400 MHz bandwidth pulsar baseband data obtained from Parkes CASPSR observations.Third,we obtain 26 subbands of 128 MHz based on CS-PFB and the simulation data,and the pulse profile of each subband by coherent dispersion,integration,and folding.Finally,the phase of each subband pulse profile is aligned by non-coherent dedispersion,and to generate a broadband pulse profile,which is basically the same as the pulse profile obtained from the original data using DSPSR.The experimental results show that the scheme for the QTT UWL receiving system is feasible,and the proposed channel algorithm in this paper is effective.

关键词： pulsars general-methods data analysis-techniques miscellaneous

Research on Channelization Techniques of Radio Astronomical Wideband Signal with Oversampled Polyphase Filter Banks

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Research in Astronomy and Astrophysics 2023年第8期23卷 188-205页

作者： Meng Zhang Hai-Long Zhang Ya-Zhou Zhang Jie Wang Shao-Cong Guo Qiao Meng Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China University of Chinese Academy of Sciences Beijing 100049China Key Laboratory of Radio Astronomy Chinese Academy of SciencesNanjing 210008China National Astronomical Data Center Beijing 100101China School of Information Science and Engineering Southeast UniversityNanjing 211100China School of Cyber Science and Engineering Qufu Normal UniversityQufu 273165China

Digital channelization decomposes a wideband signal into multiple adjacent sub-bands using Parallel Technology.Channelization can effectively reduce the pressure on the radio astronomy digital backends system and make wideband signal processing possible.Aiming at the problems of signal attenuation at sub-band edge,spectral leakage and aliasing encountered in wideband signal channelization,algorithms to reduce the problems are studied.We design a Critically Sampled Polyphase Filter Bank(CS-PFB)based on the Finite Impulse Response digital filter with a Hamming Window and systematically analyze the frequency response characteristics of the CS-PFB.Based on the channelized structure of the CS-PFB,an Over Sampled Polyphase Filter Bank(OS-PFB)is designed by data reuse,and the filtering frequency response characteristics of CS-PFB and OS-PFB are compared and analyzed.Using the wideband baseband data generated by the CASPSR(Collaboration for Astronomy Signal processing and electronics research Parkes Swinburne Recorder),we implement sub-band division and 16-band output of these data based on the 2×oversampling OS-PFB,and the problem of spectrum inversion in the sub-bands is corrected.After removing 25%of redundant data in the head and tail of each sub-band,we recombine the sub-bands into a wideband.The wideband signal is almost identical to the original observed signal.Therefore,the experimental results show that the OS-PFB can improve the channel response.For the 400 MHz baseband data of J0437-4715,we compare the pulse profile obtained from the original baseband data with the pulse profile obtained after the channelization and recombination.The phase and amplitude information of the pulse profiles are consistent,which verifies the correctness of our channelization algorithm.

关键词： (stars:)pulsars general-methods analytical-miscellaneous-methods data analysis

Redshift Dependence of the Low-energy Spectral Index of Gamma-Ray Bursts Revisited

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Research in Astronomy and Astrophysics 2023年第12期23卷 57-62页

作者： Xiao-Li Zhang Yong-Feng Huang Ze-Cheng Zou Department of Physics Nanjing UniversityNanjing 210023China School of Astronomy and Space Science Nanjing UniversityNanjing 210023China Key Laboratory of Modern Astronomy and Astrophysics(Nanjing University) Ministry of EducationNanjing 210023China Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China

A negative correlation was found to exist between the low-energy spectral index and the redshift of gamma-ray bursts(GRBs)by Amati et al.It was later confirmed by Geng&Huang and Gruber et al.,but the correlation was also found to be quite dispersive when the sample size was significantly expanded.In this study,we have established two even larger samples of GRBs to further examine the correlation.One of our samples consists of316 GRBs detected by the Swift satellite,and the other one consists of 80 GRBs detected by the Fermi satellite.It is found that there is no correlation between the two parameters for the Swift sample,but there does exist a weak negative correlation for the Fermi sample.The correlation becomes even more significant when the spectral index at the peak flux is considered.It is argued that the absence of the correlation in the Swift sample may be due to the fact that Swift has a very narrow energy response so that it could not measure the low-energy spectral index accurately enough.Further studies based on even larger GRB samples are solicited.

关键词： (stars:)gamma-ray burst general-methods statistical-catalogs

Effect of Matching Algorithm and Profile Shape on Pulsar Pulse Time of Arrival Uncertainties

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Research in Astronomy and Astrophysics 2023年第12期23卷 230-241页

作者： J.Wang J.P.W.Verbiest G.M.Shaifullah J.P.Yuan Ruhr-Universität Bochum Fakultät für Physik und AstronomieAstronomisches Institut(AIRUB)D-44801 BochumGermany Advanced Institute of Natural Sciences Beijing Normal UniversityZhuhai 519087China Fakulatät für Physik Universität BielefeldPostfach 100131D-33501 BielefeldGermany Max-Planck-Institut für Radioastronomie Auf dem Hügel 69D-53121 BonnGermany Florida Space Institute University of Central Florida12354 Research ParkwayOrlandoFL 32826USA Dipartimento di Fisica"G.Occhialini "Universitádegli Studi di Milano-BicoccaPiazza della Scienza 3I-20126 MilanoItaly INFN Sezione di Milano-BicoccaPiazza della Scienza 3I-20126 MilanoItaly Xinjiang Astronomical Observatory Chinese Academy of SciencesUrumqi 830011China Key Laboratory of Radio Astronomy Chinese Academy of SciencesNanjing 210008China INAF-Osservatorio Astronomico di Cagliari via della Scienza 509047 Selargius(CA)Italy

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.

关键词： methods data analysis-(stars:)pulsars general-methods statistical