Exploring the Dynamic Radio Sky: The Search for Slow Transients with the VLA

While synoptic surveys in the optical and at high energies have revealed a rich discovery phase space of slow transients, a similar yield is still awaited in the radio. Majority of the past blind surveys, carried out with radio interferometers, have suffered from a low yield of slow transients, ambiguous transient classifications, and contamination by false positives. The newly-refurbished Karl G. Jansky Array (Jansky VLA) offers wider bandwidths for accurate RFI excision as well as substantially-improved sensitivity and survey speed compared with the old VLA. The Jansky VLA thus eliminates the pitfalls of interferometric transient search by facilitating sensitive, wide-field, and near-real-time radio surveys and enabling a systematic exploration of the dynamic radio sky. This thesis aims at carrying out blind Jansky VLA surveys for characterizing the radio variable and transient sources at frequencies of a few GHz and on timescales between days and years. Through joint radio and optical surveys, the thesis addresses outstanding questions pertaining to the rates of slow radio transients (e.g. radio supernovae, tidal disruption events, binary neutron star mergers, stellar flares, etc.), the false-positive foreground relevant for the radio and optical counterpart searches of gravitational wave sources, and the beaming factor of gamma-ray bursts. The need for rapid processing of the Jansky VLA data and near-real-time radio transient search has enabled the development of state-of-the-art software infrastructure. This thesis has successfully demonstrated the Jansky VLA as a powerful transient search instrument, and it serves as a pathfinder for the transient surveys planned for the SKA-mid pathfinder facilities, viz. ASKAP, MeerKAT, and WSRT/Apertif.

Circumstantial Evidence for a Soft Nuclear Symmetry Energy at Suprasaturation Densities

Within an isospin- and momentum-dependent hadronic transport model, it is shown that the recent FOPI data on the pi(-)/pi(+) ratio in central heavy-ion collisions at SIS/GSI energies [Willy Reisdorf , Nucl. Phys. A 781, 459 (2007)] provide circumstantial evidence suggesting a rather soft nuclear symmetry energy E-sym(rho) at rho >= 2 rho(0) compared to the Akmal-Pandharipande-Ravenhall prediction. Some astrophysical implications and the need for further experimental confirmations are discussed.

Superfluidity in dense nuclear matter

We discuss the onset of superfluidity in neutron stars, where the model of nuclear matter is realized in a high-density and asymmetry state. In particular, we present the study of the effects of microscopic three-body forces on the proton pairing in the 1S0 channel and neutron pairing in 3PF1 channel for β-stable neutron star matter. It is found that the main effects of three-body forces are to shrink the domain of existence of the 1S0 below the threshold of the direct URCA process and to stretch the density range of the 3PF1 pairing in a broad domain so to cover most part of the neutron-star core.

Isospin dependence of nucleon (PF2)-P-3 superfluidity in asymmetric nuclear matter

We have investigated the isospin dependence of the neutron and proton (PF2)-P-3 superfluidity in isospin-asymmetric nuclear matter within the framework of the Brueckner-Hartree-Fock approach and the BCS theory. We show that the (PF2)-P-3 neutron and proton pairing gaps depend sensitively on isospin asymmetry of asymmetric nuclear matter. As the isospin asymmetry increases, the neutron (PF2)-P-3 superfluidity becomes stronger and the peak value of the neutron (PF2)-P-3 pairing gap increases rapidly. The isospin dependence of the proton (PF2)-P-3 superfluidity is shown to be opposite to the neutron one. The proton (PF2)-P-3 superfluidity becomes weaker at a higher asymmetry and it even vanishes at high enough asymmetries. At high asymmetries, the neutron (PF2)-P-3 superfluidity turns out to be much stronger than the proton one, implying that the neutron (PF2)-P-3 superfluidity is dominated in the highly asymmetric dense interior of neutron stars.

Dynamical analysis on heavy-ion fusion reactions near Coulomb barrier

The shell correction is proposed in the improved isospin dependent quantum molecular dynamics (Im-IQMD) model, which plays an important role in heavy-ion fusion reactions near Coulomb barrier. By using the ImIQMD model, the static and dynamical fusion barriers, dynamical barrier distribution in the fusion reactions are analyzed systematically. The fusion and capture excitation functions for a series of reaction systems are calculated and compared with experimental data. It is found that the fusion cross sections for neutron-rich systems increase obviously, and the strong shell effects of two colliding nuclei result in a decrease of the fusion cross sections at the sub-barrier energies. The lowering of the dynamical fusion barriers favors the enhancement of the sub-barrier fusion cross sections, which is related to the nucleon transfer and the neck formation in the fusion reactions.

Hyperon coupling dependence of hadron matter properties in relativistic mean field model

The properties of hadronic matter at beta equilibrium in a wide range of densities are described by appropriate equations of state in the framework of the relativistic mean field model. Strange meson fields, namely the scalar meson field sigma*(975) and the vector meson field sigma*(1020), are included in the present work. We discuss and compare the results of the equation of state, nucleon effective mass, and strangeness fraction obtained by adopting the TM1, TMA, and GL parameter sets for nuclear sector and three different choices for the hyperon couplings. We find that the parameter set TM1 favours the onset of hyperons most, while at high densities the GL parameter set leads to the most hyperon-rich matter. For a certain parameter set (e.g. TM1), the most hyperon-rich matter is obtained for the hyperon potential model. The influence of the hyperon couplings on the effective mass of nucleon, is much weaker than that on the nucleon parameter set. The nonstrange mesons dominate essentially the global properties of dense hyperon matter. The hyperon potential model predicts the lowest value of the neutron star maximum mass of about 1.45 M-sun to be 0.4-0.5 M-sun lower than the prediction by using the other choices for hyperon couplings.

Hyperon-hyperon interaction in relativistic mean field model

By using the new experimental data of Lambda Lambda potential, this paper has performed a full calculation for strange hadronic matter with different strangeness contents as well as its consequences on the global properties of neutron star matter in relativistic mean field model. It finds that the new weak hyperon - hyperon interaction makes the equations of state much stiffer than the result of the previous strong hyperon-hyperon interaction, and even stiffer than the result without consideration of hyperon -hyperon interaction. This new hyperon -hyperon interaction results in a maximum mass of 1.75M(circle dot) ( where M-circle dot stands for the mass of the Sun), about 0.2-0.5M(circle dot) larger than the previous prediction with the presence of hyperons. After examining carefully the onset densities of kaon condensation it finds that this new weak version of hyperon -hyperon interaction favours the occurrence of kaons in comparison with the strong one.

Antikaon condensation and in-medium kaon and antikaon production in protoneutron stars

Antikaon condensation and kaon and antikaon production in protoneutron stars are investigated in a chiral hadronic model (also referred to as the FST model in this paper). The effects of neutrino trapping on protoneutron stars are analyzed systematically. It is shown that neutrino trapping makes the critical density of K- condensation delay to higher density and (K) over bar (0) condensation not occur. The equation of state (EOS) of (proto)neutron star matter with neutrino trapping is stiffer than that without neutrino trapping, As a result, the maximum masses of (proto)neutron stars with neutrino trapping are larger than those without neutrino trapping. If hyperons are taken into account, antikaon does not form a condensate in (Proto)neutron stars. Meanwhile, the corresponding EOS becomes much softer, and the maximum masses of (proto)neutron stars are smaller than those without hyprons. Finally, our results illustrate that the Q values for K+ and K- production in (proto)neutron stars are not sensitive to neutrino trapping and inclusion of hyperons.

Dynamics of pion production in heavy-ion collisions around 1A GeV energies

Within the framework of the improved isospin-dependent quantum molecular dynamics model, the dynamics of pion emission in heavy-ion collisions in the region of 1A GeV energies as a probe of nuclear symmetry energy at suprasaturation densities is investigated systematically. The total pion multiplicities and the pi(-)/pi(+) yields are calculated for selected Skyrme parameters SkP, SLy6, Ska, and SIII and also for the cases of different stiffness of symmetry energy with the parameter SLy6. The influence of Coulomb potential, symmetry energy, and in-medium pion potential on the pion production is investigated and compared to each other by analyzing the distributions of transverse momentum and longitudinal rapidity and also the excitation functions of the total pion and the pi(-)/pi(+) ratio. The directed flow, elliptic flow, and polar-angle distributions are calculated for the cases of different collision centralities and also the various stiffnesses of the symmetry energies. A comparison of the calculations with the available experimental data is performed.

用RIMS研究低能He2+与Ar碰撞的多电子过程

用反冲离子动量谱仪研究了低能He2+与Ar碰撞的多电子交换过程。该技术的独特优势是对反冲离子末态动量的完全测量。实验上鉴别了单电子俘获SC，双电子俘获DC和转移电离TI各子过程，并得到了末态量子态布居信息，首次测量了该体系各反应道的角微分截面及直接与碰撞参数相关的信息。实验发现电子主要俘获到入射离子基态或单激发态，反冲离子处于单激发态或多激发态，并有较大几率形成空心离子。研究表明电荷交换过程中存在较强的电子-电子关联作用。角分布随反冲离子电荷态增加而变宽，并向大角度方向移动，表明碰撞参数减小，相互作用加剧。SC和DC与MCBM理论角微分截面符合很好，说明在大碰撞参数时经典近似有一定合理性。不同碰撞参数范围内反冲纵向动量分布表明，SC在碰撞参数7.2a.u.≥b≥3.6a.u.时发生机率最大，随碰撞参数减小，靶离子有不断向更高激发态过渡的趋势

三体核力对核物质中基态关联效应和中子星物质中1S0态质子超流性的影响

本论文介绍了极端条件下核物质性质研究的现状以及目前常用的几种微观核多体方法，系统描述了核物质中的基态关联效应、温度效应对单核子势的影响和同位旋非对称核物质 态中子、质子超流性，重点考虑了利用介子交换流方法建立的微观三体核力所产生的影响。利用BHF和BCS的理论方法,计算了同位旋非对称核物质中 态中子和质子的对关联能隙，着重讨论了三体核力的影响。结果表明，三体核力对同位旋非对称核物质中 态的中子超流性影响相对较小，但是对 态的质子超流性具有重要影响，其效应随总核子数密度的增大而迅速增强。随着同位旋非对称度 的增加，中子能隙向低密移动，能隙峰值逐渐增大，并且这种效果随着 的增加而逐渐减弱，而质子的情况刚好相反。另外还参与了 稳定中子星物质中超流性的研究。利用质量算子空穴线展开，通过计算不同温度和密度下的核物质中单核子势和核子有效质量，重点研究和讨论了基态关联效应和三体核力贡献对热核物质中单核子势的影响，研究表明：基态关联效应提供了一个排斥效应，温度和三体核力都削弱了基态关联效应

中子及中子星物质中的3PF2态超流性和微观三体核力效力效应

本论文介绍了当前中子及中子星物质中超流性研究的背景及现状、核多体理论Brueckner-Hartree-Fock及同位旋相关的Brueckner-Hartree-Fock方法，以及利用BHF和BCS理论计算中子及中子星物质中的对关联能隙方法。系统计算并描述了中子及中子星物质中子的3PF2态超流性，并重点考虑了利用介子交换流方法建立的微观三体核力所产生的影响。 我们的研究结果表明：三体核力对中子物质中3PF2态中子超流性有强烈的增强效应。 当在BCS能隙方程中采用自由粒子能谱近似时，三体核力使相应的对关联能隙峰值增加了77%(由0.64MeV增大到1.13MeV)；当采用自洽BHF单粒子能谱时，三体核力导致相应的对关联能隙峰值由0.22MeV增大到0.50MeV，增加了约127%。 三体核力使中子星物质中3PF2态中子超流能隙随着密度的增大而单调递增。当采用自洽BHF单粒子能谱时不考虑三体核力时，对关联能隙峰值在密度约1.9fm-3时有峰值0.19MeV。而在这个两体力导致的能隙的峰值密度，三体核力导致相应的对关联能隙由0.19MeV增大到0.36MeV

三体核力影响下的核物质状态方程及中子星物质中的中子质子超流性

本论文介绍了极端条件下核物质研究的现状以及目前常用的几种核多体方法，系统描述了冷、热非对称核物质的状态方程和刀稳定中子星物质中的15。态中子和质子超流性，特别是微观三体核力对此所产生的影响。通过引入微观三体核力，扩展了有限温度的BI．tleclcller-Hal'tree-Fock（FTBHF）理论。利用这一扩展的理沦，详细研究了同位旋非对称热核物质的状态方程、液气相变临界现象以及三体核力对此所产生的影响。在不同的中质比条件下，重点讨论了热核物质液气相变的临界温度和动力学不稳定区域的温度、同位旋相关性。由此表明，三体核力的引入在一定程度上降低了液气相变的临界温度值，在固定的温度和密度下，非对称核物质的压弧随同位旋非对称度的增加而单调的增力日，而且随着核物质温度的升高和非对称度的增加，动力学不稳定区域逐渐缩小。通过与其它理论模型（特别是Di1'ac-BHF方法）所预言的结果相比较，就目前扩展的包含三体核力修正的FTBHF理论与Dilac-BHF方法所计算的临界温度的差异问题，文中给出一种可能的解释。通过计算热核物质的单粒子结合能，给出了有限温度条件下对称能的计算方式，并且细致研究了不同温度、密度下的对称能以及三体核力在高密度区域对对称能的影响。结果表明，微观三体核力强烈影响着高密度区域的对称能，使其对温度的变化更加明显。此外，其它重要物理量（例如中子和质子的单粒子势能、有效质量等）的同位旋依赖性和温度、密度相关性在文中也被详细的讨论。利用质量算子的空穴线展井，表明了在基态关联所导致的对单核子势的重排修正项影响下的HLlgenholtz-VanHove(HVH)定理的恢复程度，并且进一步计算了中子和质子化学势。并且以包含兰体核力的FTBI-方法为基础，研究了热核物质中重排项的密度和温度依赖性并讨论了三体核力对重排项的影响。通过计算不同温度和密度下的核物质中单核子势和核子有效质量，特别是研究和讨论了基态关联效应和三体核力贡献对热核物质中单核子势的影响，表明了基态关联和三体核力对单核子势修正的重要性。利用BHF和BCS的理论方法，计算了β稳定中子星物质中处于150态的中子和质子的对关联能隙，着重研究和讨论了三体核力的影响。结果表明，三体核力对刀稳定物质中｛s0态中子超流性的影响相对较小，但是对，S0态质子超流性具有重要影响，其效应随核子数密度的增大而迅速增强。三体核力的主要作用是强烈地抑制了高密度区刀稳定中子星物质中的150态质子超流性，而且三体核力对中子星物质中，So态超流相的抑制效应主要是通过质子或中子的有效对相互作用而起作用的。

X-ray and optical studies of soft x-ray transients in M31

Soft X-ray transients (SXTs) are a subgroup of low-mass X-ray binaries consisting of a neutron star or a black hole and a companion low-mass star. SXTs exhibit a sudden outburst by increasing the luminosity from ∼ 1033 to ∼ 1036−38ergs1. After spending a few months in outburst, SXTs switch back to quiescence. Optical study of the binary system during the quiescence state of SXTs provides an opportunity to discriminate between BH binaries and neutron star binaries. The first part ot this research is composed of result of 10 years joint project between Hubble space telescope and Chandra, to study SXTs in M31. The other part of this thesis focused on the light curve of bright SXTs in M31. Disc irradiation is thought to be capable of explaining the global behaviour of the light curves of SXTs. Depending on the strength of the central X-ray emission in irradiating the disc, the light curve may exhibit an exponential or a linear decay. The model predicts that in brighter transients a transition from exponential decline to a linear one may be detectable. In this study, having excluded super-soft sources and hard X-ray transients, a sample of bright SXTs in M31 (Lpeak > 1038ergs1) has been studied. The expected change in the shape of the decay function is only observed in two of the light curves from the six light curves in the sample. Also, a systematic correlation between the shape of the light curve and the X-ray luminosity has not been seen.

The first polarimetric signatures of infrared jets in X-ray binaries

We present near-infrared linear spectropolarimetry of a sample of persistent X-ray binaries, Sco X-1, Cyg X-2, and GRS 1915+105. The slopes of the spectra are shallower than what is expected from a standard steady state accretion disk, and can be explained if the near-infrared flux contains a contribution from an optically thin jet. For the neutron star systems, Sco X-1 and Cyg X-2, the polarization levels at 2.4 mu m are 1.3% +/- 0.10% and 5.4% +/- 0.7%, respectively, which is greater than the polarization level at 1.65 mu m. This cannot be explained by interstellar polarization or electron scattering in the anisotropic environment of the accretion flow. We propose that the most likely explanation is that this is the polarimetric signature of synchrotron emission arising from close to the base of the jets in these systems. In the black hole system GRS 1915+105 the observed polarization, although high (5.0% +/- 1.2% at 2.4 mu m), may be consistent with interstellar polarization. For Sco X-1 the position angle of the radio jet on the sky is approximately perpendicular to the near-infrared position angle (electric vector), suggesting that the magnetic field is aligned with the jet. These observations may be a first step toward probing the ordering, alignment, and variability of the outflow magnetic field in a region closer to the central accreting object than is observed in the radio band.