The symmetry energy and incompressibility constrained by the observations of glitching pulsars

We investigate the masses of glitching pulsars in order to constrain their equation of state(EOS). The observations of glitches(sudden jumps in rotational frequency) may provide information on the interior physics of neutron stars. With the assumption that glitches are triggered by superfluid neutrons, the masses of glitching neutron stars can be estimated using observations of maximum glitches.Together with the observations of thermal emission from glitching pulsars Vela and J1709–4429, the slope of symmetry energy and incompressibility of nuclear matter at saturation density can be constrained.The slope of symmetry energy L should be larger than 67 MeV while the lower limit of incompressibility for symmetric nuclear matter K_0 is 215 MeV. We also obtain a relationship between L and K_0:6.173 MeV + 0.283 K_0≤ L ≤ 7.729 MeV + 0.291 K_0. The restricted EOSs are consistent with the observations of 2-solar-mass neutron stars and gravitational waves from a binary neutron star inspiral.     

Strange star candidates revised within a quark model with chiral mass scaling

We calculate the properties of static strange stars using a quark model with chiral mass scaling.The results are characterized by a large maximum mass (～ 1.6 M) and radius (～10 km).Together with a broad collection of modern neutron star models,we discuss some recent astrophysical observational data that could shed new light on the possible presence of strange quark matter in compact stars.We conclude that none of the present astrophysical observations can prove or confute the existence of strange stars.     

An Estimation of the Initial Period of Pulsars

The initial period of a pulsar is an important factor in our understanding of the formation of neutron stars and of the nature of the equation of state of neutron star matter.Up to now this quantity can only be obtained for a few pulsars for which accurate age and braking index are known.Based on the theory of the offcenter dipole emission,in which pulsars obtain theiry high velocities depending on the initial periods,we calculate the initial period using the proper motion data,Because the orbital velocity of the progenitor and asymmetric kick in the supernova explosion may also contribute to the observed velocity of the pusar,the derived values of initial periods are lower limits.For normal pulsars,the initial periods are in the range of 0.6～2.6ms.For the millisecond pulsars,the initial periods are comparable to their current periods,and the ratio between the initial period and the current period increases with the decrease of the current period.For PSR B1937 21 with the shortest period of 1.56ms,the ratio is 0.77.     

An Annular Gap Acceleration Model for γ-ray Emission of Pulsars

If the binding energy of the pulsar's surface is not so high (the case of a neutron star), both negative and positive charges will flow out freely from the surface of the star. An annular free flow model for γ-ray emission of pulsars is suggested. It is emphasized that: (1) Two kinds of acceleration regions (annular and core) need to be taken into account. The annular acceleration region is defined by the magnetic field lines that cross the null charge surface within the light cylinder. (2) If the potential drop in the annular region of a pulsar is high enough (normally the case for young pulsars), charges in both the annular and the core regions could be accelerated and produce primary gamma-rays. Secondary pairs are generated in both regions and stream outwards to power the broadband radiations. (3) The potential drop grows more rapidly in the annular region than in the core region. The annular acceleration process is a key process for producing the observed wide emission beams. (4) The advantages of both the polar cap and outer gap models are retained in this model. The geometric properties of the γ-ray emission from the annular flow are analogous to that pre-sented in a previous work by Qiao et al., which match the observations well. (5) Since charges with different signs leave the pulsar through the annular and the core regions respectively, the current closure problem can be partially solved.     

Constraints on smoothness parameter and dark energy using observational H (z) data

With large-scale homogeneity,the universe is locally inhomogeneous,clustering into stars,galaxies and larger structures.Such property is described by the smoothness parameter α which is defined as the proportion of matter in the form of intergalactic medium.If we consider the inhomogeneities over a small scale,there should be modifications of the cosmological distances compared to a homogenous model.Dyer and Roeder developed a second-order ordinary differential equation(D-R equation) that describes the angu...     

Current Flows in Pulsar Magnetospheres

The global structure of current flows in pulsar magnetosphere is investigated, with rough calculations of the circuit elements. It is emphasized that the potential of the critical field lines (the field lines that intersect the null surface at the light cylinder radius) should be the same as that of interstellar medium, and that pulsars whose rotation axes and magnetic dipole axes are parallel should be positively charged, in order to close the pulsar's current flows. The statistical relation between the radio luminosity and pulsar's electric charge (or the spindown power) may hint that the millisecond pulsars could be low-mass bare strange stars.     

Space-Time Geometry of Quark and Strange Quark Matter

We study quarkand strangequarkmatter in the contextof generalrelativity.For this purpose,we solve Einstein's field equations for quark and strange quark matter in spherical symmetric space-times. We analyze strange quark matter for the different equations of state (EOS) in the spherical symmetric space-times,thus we are able to obtain the space-time geometries of quark and strange quark matter. Also,we discuss the features of the obtained solutions. The obtained solutions are consistent with the results of Brookhaven Laboratory,i.e. the quark-gluon plasma has a vanishing shear (i.e. quark-gluon plasma is perfect).     

A relativistic model of stellar objects with core-crust-envelope division

In this work, we present a cogent and physically well-behaved solution for neutron stars envisaged with a core layer having quark matter satisfying the MIT-bag equation of state(Eo S), meso layer with Bose-Einstein condensate(BEC) matter satisfying modified BEC Eo S and an envelope having neutron fluid and Coulomb liquids satisfying quadratic Eo S. All the required physical and geometrical parameters like gravitational potentials, pressures, radial velocity, anisotropy, adiabatic index, mass function, compactification factor, and gravitational and surface redshift functions show a feasible trend and are continuous with smooth variation throughout the interior and across the regions of the star.Further, causality condition, energy conditions, static stability criterion(using Tolman-OppenheimerVolkoff equation) and Herrera cracking stability criterion are met throughout the star. The approach seems to be resulting in more realistic and accurate modeling of stellar objects, particularly realized by us for X-ray binary stars 4 U 1608–52(M = 1.7 M_⊙, R = 9.5 km) and SAX J1808.4–3658(M = 1.2 M_⊙,R = 7.2 km). Furthermore, we have ascertained that the continuity of the stability factor in all three regions of the stars demand a smaller core. As the core region of the star increases, the stability factor becomes discontinuous at all the interfaces inside the star.     

SWIFT J1749.4-2807: A neutron or quark star?

We investigate a unique accreting millisecond pulsar with X-ray eclipses,SWIFT J1749.4-2807(hereafter J1749),and try to set limits on the binary system by various methods including use of the Roche lobe,the mass-radius relations of both main sequence(MS)and white dwarf(WD)companion stars,as well as the measured mass function of the pulsar.The calculations are based on the assumption that the radius of the companion star has reached its Roche radius(or is at 90%),but the pulsar's mass has not been assumed to be a certain value.Our results are as follows.The companion star should be an MS one.For the case that the radius equals its Roche one,we have a companion star with mass M(～-)0.51 M⊙ and radius Rc(～-)0.52 R⊙,and the inclination angle is i(～-)76.5°; for the case that the radius reaches 90% of its Roche one,we have M(～-)0.43 M⊙,Re()0.44 R⊙ and i(～-)75.7°.We also obtain the mass of J1749,Mp(～-)1 M⊙,and conclude that the pulsar could be a quark star if the ratio of the critical frequency of rotation-mode instability to the Keplerian one is higher than～0.3.The relatively low pulsar mass(about～M⊙)may also challenge the conventional recycling scenario for the origin and evolution of millisecond pulsars.The results presented in this paper are expected to be tested by future observations.     

Maser Emission of Relativistic Electrons Spiralling and Drifting in Curved Magnetic Fields

Synchro-curvature radiation describes the emission from a relativistic charged par- ticle which is moving and spiralling in a curved magnetic field. We investigate the maser emission for synchro-curvature radiation including drift of the guiding center of the radiating electron. It is shown that under some conditions the absorption coefficient can be negative, so maser can happen. These conditions are different from those needed for maser emission of curvature radiation including drift of the charged particles. We point out that our results, in- cluding the emissivity, can reduce to these of curvature radiation. Previously it was found that synchro-curvature radiation can not generate maser in vacuum, but we argue that synchro- curvature radiation including drift can generate maser even in vacuum. We discuss the possi- bilities of the potential applications of the synchro-curvature maser in modeling gamma ray bursts and pulsars.     

On the magnetic fields of ultraluminous X-ray pulsars

So far quite a few ultraluminous X-ray(ULX) pulsars have been discovered.In this work,we construct a super-Eddington,magnetic accretion disk model to estimate the dipole magnetic field of eight ULX pulsars based on their observed spin-up variations and luminosities.We obtain two branches of dipole magnetic field solutions.They are distributed in the range of B～(0.156-64.5) × 10~(10) G and～(0.275-79.0) × 10~(13) G corresponding to the low-and high-B solutions respectively.The low magnetic field solutions correspond to the state that the neutron stars are far away from the spin equilibrium,and the high magnetic field solutions are close to the spin equilibrium.The ultra-strong magnetic fields derived in Be-type ULX pulsars imply that the accretion mode in Be-type ULX pulsars could be more complicated than in the persistent ULX pulsars and may not be accounted for by the magnetized accretion disk model.We suggest that the transition between the accretor and the propeller regimes may be used to distinguish between the low-and high-B magnetic field solutions in addition to the detection of the cyclotron resonance scattering features.     

Rotation Periods of Nine ROSAT Selected Solar-Type Stars

We monitored 16 X-ray selected young solar-type stars for light variation and found appreciable periodic light variability with amplitudes of a few hundredths of a magni-tude in nine of the objects. Using the method of Phase Dispersion Minimization (PDM) and Fourier analysis (software PERIOD04), the rotation periods of these stars were determined from the photometric data. The rotation periods of all nine stars are shorter than about 3days. It is suggested that, as with the Pleiades cluster, small amplitude light variations are quite common among young solar-type stars with rotation periods around 3 days or less. This gives further evidence for the spin up of solar-type stars predicted by models of angular momentum evolution of pre-main sequence stars.     

Unifying neutron star sub-populations in the supernova fallback accretion model

We employ the supernova fallback disk model to simulate the spin evolution of isolated young neutron stars(NSs). We consider the submergence of the NS magnetic fields during the supercritical accretion stage and its succeeding reemergence. It is shown that the evolution of the spin periods and the magnetic fields in this model is able to account for the relatively weak magnetic fields of central compact objects and the measured braking indices of young pulsars. For a range of initial parameters, evolutionary links can be established among various kinds of NS sub-populations including magnetars, central compact objects and young pulsars. Thus, the diversity of young NSs could be unified in the framework of the supernova fallback accretion model.     

Numerical analysis of modal tomography for solar multi-conjugate adaptive optics

Multi-conjugate adaptive optics (MCAO) can considerably extend the corrected field of view with respect to classical adaptive optics, which will benefit solar observation in many aspects. In solar MCAO, the Sun structure is utilized to provide multiple guide stars and a modal tomography approach is adopted to implement threedimensional wavefront restorations. The principle of modal tomography is briefly reviewed and a numerical simulation model is built with three equivalent turbulent layers and a different number of guide stars. Our simulation results show that at least six guide stars are required for an accurate wavefront reconstruction in the case of three layers, and only three guide stars are needed in the two layer case. Finally, eigenmode analysis results are given to reveal the singular modes that cannot be precisely retrieved in the tomography process.     

Space-Time Geometry of Quark and Strange Quark Matter

We study quark and strange quark matter in the context of general relativity. For this purpose, we solve Einstein＇s field equations for quark and strange quark matter in spherical symmetric space-times. We analyze strange quark matter for the different equations of state （EOS） in the spherical symmetric space-times, thus we are able to obtain the space-time geometries of quark and strange quark matter. Also, we discuss the features of the obtained solutions. The obtained solutions are consistent with the results of Brookhaven Laboratory, i.e. the quark-gluon plasma has a vanishing shear （i.e. quark-gluon plasma is perfect）.     

Velocity Space of Galactic O-B Stars

Based on the Hipparcos proper motions and available radial velocity data of O-B stars, we have re-examined the local kinematical structure of the young disk population of-1500 O-B stars not including the Gould-belt stars. A systematic warping motion of the stars about the direction to the Galactic center has been reconfirmed. A negative K-term implying a systematic contraction of stars in the solar vicinity has been detected. Two different distance scales are used in order to find out their impact on the kinematical parameters, and we conclude that the adopted distance scale plays an important role in characterizing the kinematical parameters at the present level of the measurement uncertainty.     

Mass transfer and loss of the massive semi-detached binary AI Crucis

AI Crucis is a short-period semi-detached massive close binary (P = 1.41771d, Sp.=B1.5) in the open cluster NGC 4103. It is a good astrophysical laboratory for investigating the formation and evolution of massive close binary stars via case A mass transfer. Orbital period variations of the system were analyzed based on one newly determined eclipse time and the others compiled from the literature. It is discovered that the orbital period of the binary is continuously increasing at a rate of dP/dt = +1.00(±0....     

A Statistical Analysis of Radio Pulsar Timing Noise

We present an analysis of the timing observations on 27 radio pulsars, collected at Hartebeesthoek Radio Astronomy Observatory (HartRAO), with time spans ranging between ～ 9 and 14yr. Our results show that the measured pulsar frequency second derivatives are non-stationary. Both the magnitude and the sign of the ■ values depend upon the choice of epoch and data span. A simple statistical analysis of the observed second time derivative of the pulse frequency (■obs) of a large sample of 391 (25 HartRAO and 366 Jodrell Bank Observatory) pulsars reveals that ■ is only marginally correlated with both the pulsar spin-d own rate ( ■) and the characteristic age (τc). We find correlation coefficients of ～ 0.20a nd-0.30 between the measured braking indices and, respectively, ■ and τc. This result reaffirms earlier conclusions that the braking indices of most radio pulsars, obtained through the standard timing technique, are strongly dominated by sustained random fluctuations in the observed pulse phase.