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Spectral Properties of Anomalous X-ray pulsars

Chinese Journal of Astronomy and Astrophysics 2003年第6期3卷 543-550页

作者： Ye Lu, Wei Wang and Yong-Heng ZhaoNational Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 National Astronomical Observatories CAS NAOC Beijing 100012 China

We examine the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variation with the spin-down rate . Based on an accretion-powered model, the influences of both the magnetic field and the mass accretion rate on the spectral properties of AXPs are addressed. We then investigate the relation between the spectral property of AXPs and mass accretion rate . The result shows that there exists a linear correlation between the photon index and the mass accretion rate: the spectral hardness increases with increasing . A possible emission mechanism for the explanation of the spectral properties of AXPs is also discussed.

关键词： pulsars: general stars: neutron X-rays: stars accretion: accretion disks

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Fast radio burst search： cross spectrum vs. auto spectrum method

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Research in Astronomy and Astrophysics 2018年第6期18卷 87-92页

作者： Lei Liu Weimin Zheng Zhen Yan Juan Zhang Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai 200030 China Key Laboratory of Radio Astronomy Chinese Academy of Sciences Nanjing 210008 China Shanghai Key Laboratory of Space Navigation and Positioning Techniques Shanghai 200030 China

The search for fast radio bursts(FRBs) is a hot topic in current radio astronomy studies. In this work, we carry out a single pulse search with a very long baseline interferometry(VLBI) pulsar observation data set using both auto spectrum and cross spectrum search methods. The cross spectrum method,first proposed in Liu et al., maximizes the signal power by fully utilizing the fringe phase information of the baseline cross spectrum. The auto spectrum search method is based on the popular pulsar software package PRESTO, which extracts single pulses from the auto spectrum of each station. According to our comparison, the cross spectrum method is able to enhance the signal power and therefore extract single pulses from data contaminated by high levels of radio frequency interference(RFI), which makes it possible to carry out a search for FRBs in regular VLBI observations when RFI is present.

关键词： techniques: interferometric radio continuum: general methods: data analysis pulsars: general

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TeV cosmic-ray proton and helium spectra in the myriad model Ⅱ

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Research in Astronomy and Astrophysics 2015年第1期15卷 15-27页

作者： Wei Liu Pierre Salati Xuelei Chen National Astronomical Observatories Chinese Academy of Science University of Chinese Academy of Sciences LAPTh Universit'e de Savoie CNRS BP 110 74941 Annecy-le-Vieux France Center of High Energy Physics Peking University

Recent observations show that the spectra of cosmic ray nuclei start to harden above ～ 102 GeV, which contradicts the conventional steady-state cosmic ray model. We had suggested that this anomaly is due to the propagation effect of cosmic rays released from local young cosmic ray sources; the total flux of cosmic rays should be computed with the Myriad Model, where a contribution from sources in the local catalog is added to the background. However, although the hardening could be elegantly explained in this model, the model parameters obtained from the fit are skewed toward a region with fast diffusion and a low supernova rate in the Galaxy, in disagreement with other observations. We further explore this model in order to set up a concordant picture. Two possible improvements related to cosmic ray sources are considered. First, instead of the usual axisymmetric disk model, we examine a spiral model for the source distribution. Second, for nearby and young sources which are necessary to explain the hardening, we allow for an energy-dependent escape. We find that a major improvement comes from incorporating an energy-dependent escape time for local sources, and with both modifications not only are the cosmic ray proton and helium anomalies resolved, but also the parameters attain values in a reasonable range compatible with other analyses.

关键词： catalogs cosmic rays pulsars: general galaxies: spiral

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On Strong Correlations between Timing Irregularities and Surface Magnetic Field of Rotation-Powered pulsars

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International Journal of Astronomy and Astrophysics 2020年第4期10卷 346-355页

作者： Evaristus Uzochukwu Iyida Christian Ikechukwu Eze Innocent Okwudili Eya Astronomy and Astrophysics Research Group Department of Physics and Astronomy University of Nigeria Nsukka Nigeria Department of Physics and Astronomy Faculty of Physical Sciences University of Nigeria Nsukka Nigeria Department of Science Laboratory Technology Faculty of Physical Sciences University of Nigeria Nsukka Nigeria

Using a large homogenous sample of Jodrell Bank Observatory (JBO) rotation-powered pulsars with derived pulsar parameter obtained from the Australian Telescope National Facility (ATNF) catalogue, we investigated the degree of statistical dependence of timing noise on surface magnetic field for our sample. The distributions of the timing irregularities parameters reveal a striking trend, in which pulsars with large timing noise parameters on average, have large surface magnetic field with up to 5 orders of magnitude. Regression analysis of the data reveals significant correlations (r ≥ 0.80) between timing noise parameters and the surface magnetic field. The implications of the observed significant relationships are discussed.

关键词： Methods: Statistical Stars: Neutron pulsars: general

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