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Universe
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A New Horizon of Pulsar and Neutron Star: The 55-Year...
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A New Horizon of Pulsar and Neutron Star: The 55-Year Anniversary

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Compact Objects".

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 4181

Special Issue Editors

Prof. Dr. Chengmin Zhang

E-Mail Website
Guest Editor
B231 National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China
Interests: pulsar; neutron star; magnetar; millisecond pulsar and accreting X-ray binary; compact object; gravitational wave; fast radio burst
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. David Blaschke

E-Mail Website
Guest Editor
1. Institute of Theoretical Physics, University of Wroclaw, 50-204 Wroclaw, Poland
2. Center for Advanced Systems Understanding (CASUS), D-02826 Görlitz, Germany
3. Helmholtz-Zentrum Dresden-Rossendorf (HZDR), D-1328 Dresden, Germany
Interests: quantum field theory; quantum statistics; quark gluon plasma; heavy ion collisions; compact stars
Special Issues, Collections and Topics in MDPI journals
Dr. Jérôme Pétri

E-Mail Website
Co-Guest Editor
Observatoire Astronomique de Strasbourg, Université de Strasbourg, 67000 Strasbourg, France
Interests: neutron stars; pulsar magnetosphere and wind; relativistic plasmas; electromagnetism; general relativity; radiative processes; numerical methods
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Fifty-five years have passed since the first pulsar was discovered in 1967, while astronomers discovered more than 3,500 pulsars, including many types of neutron stars found in various electromagnetism (EM) bands, on the basis of which a number of theoretical models have been proposed to explain the observed phonomena. Fantasticaly, the pulsars have become the natural laboratories for testing the fundamental theories of physics, e.g., nuclear and particle physics, EM wave and plasma interaction, together with neutrinos, high-energy cosmic rays, general relativity and gravitational wave as part of the multi-messenger astronomy.

The aim of this Special Issue is mainly to review the current developments, and to investigate the novel ideas and future perspectives, which brings together various topics to present a whole picture of pulsars and neutron stars (NSs), by putting all species of pulsar zoo into a unified description. Although much progress has been made, a large number of pulsar topics still need further explorations, such as, the evolution of pulsar magnetic field and its structure, spin period, radiation mechanism, thermal radiation, millisecond pulsar and binary star systems, long-period pulsars, magnetars, fast radio bursts, young pulsars, pulsar wind nebula, proto-neutron-star and supernova explosions, various NS formations and EOSs, the minimum and maximum mass of NS, glitch, braking index, CCO and isolated NS, accreting X-ray pulsars, NS transients, high/low-mass X-ray binaries and bursts, and so on. In addition, it is also encouraged for proposing new ideas on the enhancement and progress of pulsar and neutron star astrophysics.

Prof. Dr. Chengmin Zhang
Prof. Dr. David Blaschke
Dr. Jérôme Pétri
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • pulsar
  • neutron star
  • magnetar
  • X-ray binary
  • compact object
  • gravitational wave

Published Papers (4 papers)

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Research

15 pages, 5835 KiB  
Article
A New Solution of the Pulsar Equation
by Ioannis Contopoulos, Ioannis Dimitropoulos, Dimitris Ntotsikas and Konstantinos N. Gourgouliatos
Universe 2024, 10(4), 178; https://doi.org/10.3390/universe10040178 - 12 Apr 2024
Viewed by 394
Abstract
We present the first new type of solution of the pulsar equation since 1999. In it, the whole magnetosphere is confined inside the light cylinder and an electrically charged layer wraps around it and holds it together. The reason this new solution has [...] Read more.
We present the first new type of solution of the pulsar equation since 1999. In it, the whole magnetosphere is confined inside the light cylinder and an electrically charged layer wraps around it and holds it together. The reason this new solution has never been obtained before is that all current time-dependent simulations are initialized with a vacuum dipole configuration that extends to infinity; thus, their final steady-state solution also extends to infinity. Under special conditions, such a confined configuration may be attained when the neutron star first forms in the interior of a collapsing star during a supernova explosion, or when it accretes from an external wind or disk from a donor star. It is shown that this new maximally closed non-decelerating solution is the limit of a continuous sequence of standard magnetospheres with open and closed field lines when the amount of open field lines gradually drops to zero. The minimum energy solution in this sequence is a standard magnetosphere in which the closed field line region extends up to about 80% of the light cylinder. We estimate that the released energy when the new solution transitions to the minimum energy one is enough to power a fast radio burst. Full article
(This article belongs to the Special Issue A New Horizon of Pulsar and Neutron Star: The 55-Year Anniversary)
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23 pages, 2255 KiB  
Article
Mass Distribution and Maximum Mass of Neutron Stars: Effects of Orbital Inclination Angle
by Lívia S. Rocha, Jorge E. Horvath, Lucas M. de Sá, Gustavo Y. Chinen, Lucas G. Barão and Marcio G. B. de Avellar
Universe 2024, 10(1), 3; https://doi.org/10.3390/universe10010003 - 21 Dec 2023
Viewed by 980
Abstract
Matter at ultra-high densities finds a physical realization inside neutron stars. One key property is their maximum mass, which has far-reaching implications for astrophysics and the equation of state of ultra dense matter. In this work, we employ Bayesian analysis to scrutinize the [...] Read more.
Matter at ultra-high densities finds a physical realization inside neutron stars. One key property is their maximum mass, which has far-reaching implications for astrophysics and the equation of state of ultra dense matter. In this work, we employ Bayesian analysis to scrutinize the mass distribution and maximum mass threshold of galactic neutron stars. We compare two distinct models to assess the impact of assuming a uniform distribution for the most important quantity, the cosine of orbital inclination angles (i), which has been a common practice in previous analyses. This prevailing assumption yields a maximum mass of 2.25 M⊙ (2.15–3.32 M⊙ within 90% confidence), with a strong peak around the maximum value. However, in the second model, which indirectly includes observational constraints of i, the analysis supports a mass limit of 2.56−0.58+0.87M⊙ (2σ uncertainty), a result that points in the same direction as some recent results gathered from gravitational wave observations, although their statistics are still limited. This work stresses the importance of an accurate treatment of orbital inclination angles, and contributes to the ongoing debate about the maximum neutron star mass, further emphasizing the critical role of uncertainties in the individual neutron star mass determinations. Full article
(This article belongs to the Special Issue A New Horizon of Pulsar and Neutron Star: The 55-Year Anniversary)
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15 pages, 509 KiB  
Article
Zeeman Splitting of Torsional Oscillation Frequencies of Magnetars
by Dmitry Yakovlev
Universe 2023, 9(12), 504; https://doi.org/10.3390/universe9120504 - 30 Nov 2023
Viewed by 1025
Abstract
Magnetars form a special class of neutron stars possessing superstrong magnetic fields and demonstrating power flares triggered by these fields. Observations of such flares reveal the presence of quasi-periodic oscillations (QPOs) at certain frequencies; they are thought to be excited in the flares. [...] Read more.
Magnetars form a special class of neutron stars possessing superstrong magnetic fields and demonstrating power flares triggered by these fields. Observations of such flares reveal the presence of quasi-periodic oscillations (QPOs) at certain frequencies; they are thought to be excited in the flares. QPOs carry potentially important information on magnetar structure, magnetic field, and mechanisms of magnetar activity. We calculate frequencies of torsional (magneto-elastic) oscillations of the magnetar crust treating the magnetic field effects in the first order of perturbation theory. The theory predicts the splitting of non-magnetic oscillation frequencies into Zeeman components. Zeeman splitting of the torsional oscillation spectrum of magnetars was suggested, clearly described and estimated by Shaisultanov and Eichler (2009), but their work has not been given considerable attention. To extend it, we suggest the technique of calculating oscillation frequencies, including Zeeman splitting at not too strong magnetic fields for arbitrary magnetic field configuration. Zeeman splitting enriches the oscillation spectrum and simplifies the theoretical interpretation of observations. We calculate several low-frequency oscillations of magnetars with a pure dipole magnetic field in the crust. The results qualitatively agree with the low-frequency QPOs detected in the hyperflare of SGR 1806–20 and in the giant flare of SGR 1900+14. Full article
(This article belongs to the Special Issue A New Horizon of Pulsar and Neutron Star: The 55-Year Anniversary)
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20 pages, 8469 KiB  
Article
Sparsity and M-Estimators in RFI Mitigation for Typical Radio Astrophysical Signals
by Hao Shan, Ming Jiang, Jianping Yuan, Xiaofeng Yang, Wenming Yan, Zhen Wang and Na Wang
Universe 2023, 9(12), 488; https://doi.org/10.3390/universe9120488 - 23 Nov 2023
Viewed by 1022
Abstract
In this paper, radio frequency interference (RFI) mitigation by robust maximum likelihood estimators (M-estimators) for typical radio astrophysical signals of, e.g., pulsars and fast radio bursts (FRBs), will be investigated. The current status reveals several defects in signal modeling, manual factors, and a [...] Read more.
In this paper, radio frequency interference (RFI) mitigation by robust maximum likelihood estimators (M-estimators) for typical radio astrophysical signals of, e.g., pulsars and fast radio bursts (FRBs), will be investigated. The current status reveals several defects in signal modeling, manual factors, and a limited range of RFI morphologies. The goal is to avoid these defects while realizing RFI mitigation with an attempt at feature detection for FRB signals. The motivation behind this paper is to combine the essential signal sparsity with the M-estimators, which are pertinent to the RFI outliers. Thus, the sparsity of the signals is fully explored. Consequently, typical isotropic and anisotropic features of multichannel radio signals are accurately approximated by sparse transforms. The RFI mitigation problem is thus modeled as a sparsity-promoting robust nonlinear estimator. This general model can reduce manual factors and is expected to be effective in mitigating most types of RFI, thus alleviating the defects. Comparative studies are carried out among three classes of M-estimators combined with several sparse transforms. Numerical experiments focus on real radio signals of several pulsars and FRB 121102. There are two discoveries in the high-frequency components of FRB 121102-11A. First, highly varying narrow-band isotropic flux regions of superradiance are discovered. Second, emission centers revealed by the isotropic features can be completely separated in the time axis. The results have demonstrated that the M-estimator-based sparse optimization frameworks show competitive results and have potential application prospects. Full article
(This article belongs to the Special Issue A New Horizon of Pulsar and Neutron Star: The 55-Year Anniversary)
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