We present a systematic analysis of the complete set of observations of the neutron star low-mass X-ray binary 4U1608-52 obtained by the Rossi X-ray Timing Explorer's Proportional Counter Array. We study the spectral and fast-time variability properties of the source in order to determine the mass and spin of the neutron star via the relativistic precession model, and find 24 observations containing usable sets of the necessary three quasi-periodic oscillations (triplets) with which to accomplish this task, along with a further 7 observations containing two of the three quasi-periodic oscillations each. We calculate the spin and mass of the source for each of the triplets, and find that they give physically realistic estimates clustering in the spin range $0.19 < a < 0.35$ and mass range $2.15 < M/\textrm{M}_{\odot} < 2.6$. Neutron stars present environments for studying matter under the most extreme conditions of pressure and density; as their equation of state is not yet known, accurate measurements of their mass and spin will eventually allow for the discrimination between various models. We discuss the implications of our findings in the context of equation of state predictions, physically allowed spin ranges, emission proximity to the innermost stable circular orbit and possible model inaccuracies.
The influence of small-scale magnetic field on the evolution of inclination angle and precession damping in the framework of 3-component model of neutron star
Her X-1/HZ Her is one of the best studied accreting X-ray pulsars. In addition to the pulsating and orbital periods, the X-ray and optical light curves of the source exhibit an almost periodic 35-day variability caused by a precessing accretion disk. The nature of the observed long-term stability of the 35-day cycle has been debatable. The X-ray pulse frequency of Her X-1 measured by the Fermi/GBM demonstrates periodical variations with X-ray flux at the Main-on state of the source. We explain the observed periodic sub-microsecond pulse frequency changes by the free precession of a triaxial ne…
Theoretical Constraints on Neutron Star Superfluidity from Her X-1 Precession
School of Physics and Astronomy, Tel Aviv University（特拉维夫大学物理与天文学学院）；Sternberg Astronomical Institute, Lomonosov Moscow State University（罗蒙诺索夫莫斯科大学斯登伯格天文研究所）
Her X-1的观测揭示了其35天超轨道周期中通量、偏振度和偏振角的相关性，表明超流体内壳的进动可能由近自由进动驱动，这对超流体动力学提出了新的挑战。
Testing the relativistic precession model using low frequency and kHz quasi-periodic oscillations in neutron star low mass X-ray binaries with known spin
Reprocessing of primary X-ray emission in the accretion disk of black hole X-ray binaries (BHXRBs) produces the reflection spectrum, with the characteristic Fe K$α$ fluorescence line. Strong low frequency quasi-periodic oscillations (QPOs) are observed from BHXRBs, and the dependence of QPO properties (e.g., phase-lag) on the inclination angle suggests that the observed QPO may be associated with a geometrical effect, e.g., the precession of the X-ray source due to frame-dragging near the spining black hole. Here, in the scenario of Lense-Thirring precession of the X-ray source, we use a Monte…
The discovery of neutron stars powering several ultraluminous X-ray sources (ULXs) raises important questions about the nature of the underlying population. In this paper we build on previous work studying simulated populations by incorporating a model where the emission originates from a precessing, geometrically beamed wind-cone, created by a super-critical inflow. We obtain estimates -- independent of the prescription for the precession period of the wind -- for the relative number of ULXs that are potentially visible (persistent or transient) for a range of underlying factors such as the r…
A deformed neutron star (NS) will precess if the instantaneous spin axis and the angular momentum are not aligned. Such a precession can produce continuous gravitational waves (GWs) and modulate electromagnetic pulse signals of pulsars. In this contribution we extend our previous work in a more convenient parameterization. We treat NSs as rigid triaxial bodies and give analytical solutions for angular velocities and Euler angles. We summarize the general GW waveforms from freely precessing triaxial NSs and use Taylor expansions to obtain waveforms with a small wobble angle. For pulsar signals,…
Lense-Thirring precession of neutron-star accretion flows: Relativistic versus classical precession
Silesian University in Opava（奥帕瓦西里西亚大学）；Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）
General relativistic effects in the spacetime around the massive astrophysical objects can be captured using a spinning test gyro orbiting around the object in a circular geodesic. This article discusses how the tidal disruption due to a companion object affects the precession frequency of a spinning gyro orbiting around a compact astrophysical object. The precession frequency is studied in a region of space around the central object using a perturbative approach. In this study, the central object is either a neutron star or a white dwarf. The gyro is any planetary or asteroid-like object orbi…
We describe a new kind of resonance occuring in relativistic three-body hierarchical systems: the precession resonance, occuring when the relativistic precession timescale of a binary equals the period of a distant perturber. We find that, contrary to what most previous studies assume, it can lead to an exponential increase of eccentricity of the binary even when relativistic precession dominates the quadrupolar perturbation. The resonance may happen in the observation band of LISA or change the eccentricity distribution of triples. We discuss the physics of the resonance, showing that it main…
Quantifying the impact of relativistic precession on tidal disruption event light curves
Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University（查理大学数学与物理学院理论物理研究所）；Department of Physics and Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学物理学系与哥伦比亚天体物理实验室）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理中心）；Department of Physics and Astronomy, Purdue University（普渡大学物理与天文系）；Hamburger Sternwarte, Universität Hamburg（汉堡大学汉堡天文台）；The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University（斯德哥尔摩大学阿尔巴诺瓦天体物理奥斯卡·克莱因中心）
The Standard-Model Extension (SME) is an effective-field-theoretic framework that catalogs all Lorentz-violating field operators. The anisotropic correction from the minimal gravitational SME to Newtonian gravitational energy for spheroids is studied, and the rotation of rigid spheroids is solved with perturbation method and numerical approach. The well-known forced precession solution given by Nordtvedt in the parameterized post-Newtonian formalism is recovered and applied to two observed solitary millisecond pulsars to set bounds on the coefficients for Lorentz violation in the SME framework…
Young neutron stars (NSs) have magnetic fields $B$ in the range $10^{12}-10^{15}$ G, believed to be generated by dynamo action at birth. We argue that such a dynamo is actually too inefficient to explain the strongest of these fields. Dynamo action in the mature star is also unlikely. Instead we propose a promising new precession-driven dynamo and examine its basic properties, as well as arguing for a revised mean-field approach to NS dynamos. The precession-driven dynamo could also play a role in field generation in main-sequence stars.
