arXiv subjects

Xiang-Dong Li

Publications and source records attributed to Xiang-Dong Li.

At least 145 records · Page 8Linked to original sources

arXiv2015

The orbital period evolution of the supersoft X-ray source CAL 87

CAL 87 is one of the best known supersoft X-ray sources. However, the measured masses, orbital period and orbital period evolution of CAL 87 cannot be addressed by the standard thermal-timescale mass-transfer model for supersoft X-ray sources. In this work we explore the orbital evolution of CAL 87 with both analytic and numerical methods. We demonstrate that the characteristics mentioned above can be naturally accounted for by the excited-wind-driven mass-transfer model.

astro-ph.HE↗

arXiv2015

On the evolution of a fossil disk around neutron stars originating from merging white dwarfs

Numerical simulations suggest that merging double white dwarfs (WDs) may produce a newborn neutron star surrounded by a fossil disk. We investigate the evolution of the fossil disk following the coalescence of double WDs. We demonstrate that the evolution can be mainly divided into four phases: the slim disk phase (with time $\lesssim$ 1 yr), the inner slim plus outer thin disk phase ($\sim 10-\DP{6}$ yr), the thin disk phase ($\sim \DP{2}-\DP{7}$ yr), and the inner advection-dominated accretion flow plus outer thin disk phase, given the initial disk mass $\sim 0.05-0.5\,M_{\sun}$ and the disk formation time $10^{-3}-1$ s. Considering possible wind mass loss from the disk, we present both analytic formulae and numerically calculated results for the disk evolution, which is sensitive to the condition that determines the location of the outer disk radius. The systems are shown to be very bright in X-rays in the early phase, but quickly become transient within $\lesssim$ 100 yr, with peak luminosities decreasing with time. We suggest that they might account for part of the very faint X-ray transients around the Galactic center region, which generally require a very low mass transfer rate.

astro-ph.HE↗

arXiv2015

Evolution of Transient Low-Mass X-ray Binaries to Redback Millisecond Pulsars

Redback millisecond pulsars (hereafter redbacks) are a sub-population of eclipsing millisecond pulsars in close binaries. The formation processes of these systems are not clear. The three pulsars showing transitions between rotation- and accretion-powered states belong to both redbacks and transient low-mass X-ray binaries (LMXBs), suggesting a possible evolutionary link between the them. Through binary evolution calculations, we show that the accretion disks in almost all LMXBs are subject to the thermal-viscous instability during certain evolutionary stages, and the parameter space for the disk instability covers the distribution of known redbacks in the orbital period - companion mass plane. We accordingly suggest that the abrupt reduction of the mass accretion rate during quiescence of transient LMXBs provides a plausible way to switch on the pulsar activity, leading to the formation of redbacks, if the neutron star has been spun up to be an energetic millisecond pulsar. We investigate the evolution of redbacks, taking into account the evaporation feedback, and discuss its possible influence on the formation of black widow millisecond pulsars.

astro-ph.HE↗

arXiv2015

Super-Strong Magnetic Fields of Neutron Stars in Be X-Ray Binaries Estimated with New Torque and Magnetosphere Models

We re-estimate the surface magnetic fields of neutron stars (NSs) in Be X-ray binaries (BeXBs) with different models of torque, improved beyond Klus et al. (2014). In particular, a new torque model (Dai \& Li 2006) is applied to three models of magnetosphere radius. Unlike the previous models, the new torque model does not lead to divergent results for any fastness parameter. The inferred surface magnetic fields of these NSs for the two compressed magnetosphere models are much higher than that for the uncompressed magnetosphere model. The new torque model using the compressed-magnetosphere radius (Shi, Zhang \& Li 2014) leads to unique solutions near spin equilibrium in all cases, unlike other models that usually give two branches of solutions. Although our conclusions are still affected by the simplistic assumptions about the magnetosphere radius calculations, we show several groups of possible surface magnetic field values with our new models when the interaction between the magnetosphere and the infalling accretion plasma is considered. The estimated surface magnetic fields for NSs BeXBs in the Large Magellanic Cloud, the Small Magellanic Cloud and the Milk Way are between the quantum critical field and the maximum "virial" value by the spin equilibrium condition.

astro-ph.HE↗

arXiv2015

On the Law of Large Numbers for the empirical measure process of Generalized Dyson Brownian motion

We study the generalized Dyson Brownian motion (GDBM) of an interacting $N$-particle system with logarithmic Coulomb interaction and general potential $V$. Under reasonable condition on $V$, we prove the existence and uniqueness of strong solution to SDE for GDBM. We then prove that the family of the empirical measures of GDBM is tight on $\mathcal {C}([0,T],\mathscr{P}(\mathbb{R}))$ and all the large $N$ limits satisfy a nonlinear McKean-Vlasov equation. Inspired by previous works due to Biane and Speicher, Carrillo, McCann and Villani, we prove that the McKean-Vlasov equation is indeed the gradient flow of the Voiculescu free entropy on the Wasserstein space of probability measures over $\mathbb{R}$. Using the optimal transportation theory, we prove that if $V"\geq K$ for some constant $K\in \mathbb{R}$, the McKean-Vlasov equation has a unique weak solution. This proves the Law of Large Numbers and the propagation of chaos for the empirical measures of GDBM. Finally, we prove the longtime convergence of the McKean-Vlasov equation for $C^2$-convex potentials $V$.

math.PR↗

arXiv2015

A Strange Star Scenario for the Formation of Eccentric Millisecond Pulsar/Helium White Dwarf Binaries

According to the recycling scenario, millisecond pulsars (MSPs) have evolved from low-mass X-ray binaries (LMXBs). Their orbits are expected to be circular due to tidal interactions during the binary evolution, as observed in most of the binary MSPs. There are some peculiar systems that do not fit this picture. Three recent examples are PSRs J2234$+$06, J1946$+$3417 and J1950$+$2414, all of which are MSPs in eccentric orbits but with mass functions compatible with expected He white dwarf companions. It has been suggested these MSPs may have formed from delayed accretion-induced collapse of massive white dwarfs, or the eccentricity may be induced by dynamical interaction between the binary and a circumbinary disk. Assuming that the core density of accreting neutron stars in LMXBs may reach the density of quark deconfinement, which can lead to phase transition from neutron stars to strange quark stars, we show that the resultant MSPs are likely to have an eccentric orbit, due to the sudden loss of the gravitational mass of the neutron star during the transition. The eccentricities can be reproduced with a reasonable estimate of the mass loss. This scenario might also account for the formation of the youngest known X-ray binary Cir X$-$1, which also possesses a low-field compact star in an eccentric orbit.

astro-ph.HE↗

arXiv2015

Formation of Black Hole Low-Mass X-ray Binaries

The majority of known Galactic black holes reside in low-mass X-ray binaries. They are rare and fascinating objects, providing unique information on strong gravity, accretion disc physics, and stellar and binary evolution. There is no doubt that our understanding of the formation of black hole low-mass X-ray binaries has significantly advanced in the past decade. However, some key issues are still unresolved. In this paper we briefly summarize the observational clues and theoretical progress on the formation of black hole low-mass X-ray binaries.

astro-ph.HE↗

arXiv2015

A Population of Ultraluminous X-ray Sources with An Accreting Neutron Star

Most ultraluminous X-ray sources (ULXs) are believed to be X-ray binary systems, but previous observational and theoretical studies tend to prefer a black hole rather than a neutron star accretor. The recent discovery of 1.37 s pulsations from the ULX M82 X-2 has established its nature as a magnetized neutron star. In this work we model the formation history of neutron star ULXs in an M82- or Milky Way-like galaxy, by use of both binary population synthesis and detailed binary evolution calculations. We find that the birthrate is around $10^{-4}\, \rm yr^{-1}$ for the incipient X-ray binaries in both cases. We demonstrate the distribution of the ULX population in the donor mass - orbital period plane. Our results suggest that, compared with black hole X-ray binaries, neutron star X-ray binaries may significantly contribute to the ULX population, and high-mass and intermediate-mass X-ray binaries dominate the neutron star ULX population in M82- and Milky Way-like galaxies, respectively.

astro-ph.HE↗

arXiv2014

Formation of Binary Millisecond Pulsars by Accretion-Induced Collapse of White Dwarfs under Wind-Driven Evolution

Accretion-induced collapse of massive white dwarfs (WDs) has been proposed to be an important channel to form binary millisecond pulsars (MSPs). Recent investigations on thermal timescale mass transfer in WD binaries demonstrate that the resultant MSPs are likely to have relatively wide orbit periods ($\gtrsim 10$ days). Here we calculate the evolution of WD binaries taking into account the excited wind from the companion star induced by X-ray irradiation of the accreting WD, which may drive rapid mass transfer even when the companion star is less massive than the WD. This scenario can naturally explain the formation of the strong-field neutron star in the low-mass X-ray binary 4U 1822$-$37. After AIC the mass transfer resumes when the companion star refills its Roche lobe, and the neutron star is recycled due to mass accretion. A large fraction of the binaries will evolve to become binary MSPs with a He WD companion, with the orbital periods distributed between $\gtrsim 0.1$ day and $\lesssim 30$ days, while some of them may follow the cataclysmic variable-like evolution towards very short orbits. If we instead assume that the newborn neutron star appears as an MSP and part of its rotational energy is used to ablate its companion star, the binaries may also evolve to be the redback-like systems.

astro-ph.HE↗

arXiv2014

Common Envelope Mechanisms: Constraints from the X-ray Luminosity Function of High Mass X-ray Binaries

We use the measured X-ray luminosity function (XLF) of high-mass X-ray binaries (HMXBs) in nearby star-forming galaxies to constrain the common envelope (CE) mechanisms, which play a key role in governing the binary evolution. We find that the XLF can be reproduced quite closely under both CE mechanisms usually adopted, i.e., the $α_{\rm CE}$ formalism and the $γ$ algorithm, with a reasonable range of parameters considered. Provided that the parameter combination is the same, the $γ$ algorithm is likely to produce more HMXBs than the $α_{\rm CE}$ formalism, by a factor of up to $\sim$ 10. In the framework of the $α_{\rm CE}$ formalism, a high value of $α_{\rm CE}$ is required to fit the observed XLF, though it does not significantly affect the global number of the HMXB populations. We present the detailed components of the HMXB populations under the $γ$ algorithm and compare them with those in Zuo et al. and observations. We suggest the distinct observational properties, as well as period distributions of HMXBs, may provide further clues to discriminate between these two types of CE mechanisms.

astro-ph.HE↗

arXiv2014

Hamilton's Harnack inequality and the $W$-entropy formula on complete Riemannian manifolds

In this paper, we prove Hamilton's Harnack inequality and the gradient estimates of the logarithmic heat kernel for the Witten Laplacian on complete Riemainnian manifolds. As applications, we prove the $W$-entropy formula for the Witten Laplacian on complete Riemannian manifolds, and prove a family of logarithmic Sobolev inequalities on complete Riemannian manifolds with natural geometric condition.

math.PR↗

arXiv2014

$W$-entropy formula for the Witten Laplacian on manifolds with time dependent metrics and potentials

In this paper, we develop a new approach to prove the $W$-entropy formula for the Witten Laplacian via warped product on Riemannian manifolds and give a natural geometric interpretation of a quantity appeared in the $W$-entropy formula. Then we prove the $W$-entropy formula for the Witten Laplacian on compact Riemannian manifolds with time dependent metrics and potentials, and derive the $W$-entropy formula for the backward heat equation associated with the Witten Laplacian on compact Riemannian manifolds equipped with Lott's modified Ricci flow. We also extend our results to complete Riemannian manifolds with negative $m$-dimensional Bakry-Emery Ricci curvature, and to compact Riemannian manifolds with $K$-super $m$-dimensional Bakry-Emery Ricci flow. As application, we prove that the optimal logarithmic Sobolev constant on compact manifolds equipped with the $K$-super $m$-dimensional Bakry-Emery Ricci flow is decreasing in time.

math.DG↗

arXiv2014

On the formation of Be stars through binary interaction

Be stars are rapidly rotating B type stars. The origin of their rapid rotation is not certain, but binary interaction remains to be a possibility. In this work we investigate the formation of Be stars resulting from mass transfer in binaries in the Galaxy. We calculate the binary evolution with both stars evolving simultaneously and consider different possible mass accretion histories for the accretor. From the calculated results we obtain the critical mass ratios $q_{\rm cr}$ that determine the stability of mass transfer. We also numerically calculate the parameter $λ$ in common envelope evolution, and then incorporate both $q_{\rm cr}$ and $λ$ into the population synthesis calculations. We present the predicted numbers and characteristics of Be stars in binary systems with different types of companions, including helium stars, white dwarfs, neutron stars, and black holes. We find that in Be/neutron star binaries the Be stars can have a lower limit of mass $ \sim 8 M_{\odot}$ if they are formed by stable (i.e., without the occurrence of common envelope evolution) and nonconservative mass transfer. We demonstrate that isolated Be stars may originate from both mergers of two main-sequence stars and disrupted Be binaries during the supernova explosions of the primary stars, but mergers seem to play a much more important role. Finally the fraction of Be stars which have involved binary interactions in all B type stars can be as high as $ \sim 13%-30% $, implying that most of Be stars may result from binary interaction.

astro-ph.HE↗

arXiv2014

Formation of Millisecond Pulsars with Low-Mass Helium White Dwarf Companions in Very Compact Binaries

Binary millisecond pulsars (BMSPs) are thought to have evolved from low-mass X-ray binaries (LMXBs). If the mass transfer in LMXBs is driven by nuclear evolution of the donor star, the final orbital period is predicted to be well correlated with the mass of the white dwarf (WD), which is the degenerate He core of the donor. Here we show that this relation can be extended to very small WD mass ($\sim 0.14-0.17\,M_\odot$) and narrow orbital period (about a few hours), mainly depending on the metallicities of the donor stars. There is also discontinuity in the relation, which is due to the temporary contraction of the donor when the H-burning shell crosses the hydrogen discontinuity. BMSPs with low-mass He WD companions in very compact binaries can be accounted for if the progenitor binary experienced very late Case A mass transfer. The WD companion of PSR J1738+0333 is likely to evolve from a Pop~II star. For PSR J0348+0432, to explain its extreme compact orbit in the Roche lobe-decoupling phase, even lower metallicity ($Z=0.0001$) is required.

astro-ph.HE↗

arXiv2014

The Magneto Hydro Dynamical Model of KHz Quasi Periodic Oscillations in Neutron Star Low Mass X-ray Binaries (II)

We study the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low mass X-ray binaries (LMXBs) with a new magnetohydrodynamics (MHD) model, in which the compressed magnetosphere is considered. The previous MHD model (Shi \& Li 2009) is re-examined and the relation between the frequencies of the kHz QPOs and the accretion rate in LMXBs is obtained. Our result agrees with the observations of six sources (4U 0614+09, 4U 1636--53, 4U 1608--52, 4U 1915--15, 4U 1728--34, XTE 1807--294) with measured spins. In this model the kHz QPOs originate from the MHD waves in the compressed magnetosphere. The single kHz QPOs and twin kHz QPOs are produced in two different parts of the accretion disk and the boundary is close to the corotation radius. The lower QPO frequency in a frequency-accretion rate diagram is cut off at low accretion rate and the twin kHz QPOs encounter a top ceiling at high accretion rate due to the restriction of innermost stable circular orbit.

astro-ph.HE↗

arXiv2014

On the Common Envelope Efficiency

In this work, we try to use the apparent luminosity versus displacement (i.e., $L_{\rm X}$ vs. $R$) correlation of high mass X-ray binaries (HMXBs) to constrain the common envelope (CE) efficiency $α_{\rm CE}$, which is a key parameter affecting the evolution of the binary orbit during the CE phase. The major updates that crucial for the CE evolution include a variable $λ$ parameter and a new CE criterion for Hertzsprung gap donor stars, both of which are recently developed. We find that, within the framework of the standard energy formula for CE and core definition at mass $X=10$\%, a high value of $α_{\rm CE}$, i.e., around 0.8-1.0, is more preferable, while $α_{\rm CE}< \sim 0.4$ likely can not reconstruct the observed $L_{\rm X}$ vs. $R$ distribution. However due to an ambiguous definition for the core boundary in the literature, the used $λ$ here still carries almost two order of magnitude uncertainty, which may translate directly to the expected value of $α_{\rm CE}$. We present the detailed components of current HMXBs and their spatial offsets from star clusters, which may be further testified by future observations of HMXB populations in nearby star-forming galaxies.

astro-ph.HE↗

arXiv2014

Discovery of the transient magnetar 3XMM J185246.6+003317 near supernova remnant Kesteven 79 with XMM-Newton

We report the serendipitous discovery with XMM-Newton that 3XMM J185246.6+003317 is an 11.56 s X-ray pulsar located 1' away from the southern boundary of supernova remnant Kes 79. The spin-down rate of 3XMM J185246.6+003317 is $<1.1\times 10^{-13}$ s s$^{-1}$, which, together with the long period P=11.558714(2) s, indicates a dipolar surface magnetic field of $<3.6\times 10^{-13}$ G, a characteristic age of $>1.7$ Myr, and a spin-down luminosity of $<2.8\times 10^{30}$ erg s$^{-1}$. The X-ray spectrum of the source is best-fitted with a resonant Compton scattering model, and can be also adequately described by a blackbody model. The observations covering a seven month span from 2008 to 2009 show variations in the spectral properties of the source, with the luminosity decreasing from $2.7\times 10^{34}$ erg s$^{-1}$ to $4.6 \times 10^{33}$ erg s$^{-1}$, along with a decrease of the blackbody temperature from $kT\approx 0.8$ keV to $\approx0.6$ keV. The X-ray luminosity of the source is higher than its spin-down luminosity, ruling out rotation as a power source. The combined timing and spectral properties, the non-detection of any optical or infrared counterpart, together with the lack of detection of the source in archival X-ray data prior to the 2008 XMM-Newton observation, point to this source being a newly discovered transient low-B magnetar undergoing an outburst decay during the XMM-Newton observations. The non-detection by Chandra in 2001 sets an upper limit $4\times 10^{32}$ erg s$^{-1}$ to the quiescent luminosity of 3XMM J185246.6+003317. Its period is the longest among currently known transient magnetars. The foreground absorption toward 3XMM J185246.6+003317 is similar to that of Kes 79, suggesting a similar distance of $\sim$7.1 kpc.

astro-ph.HE↗

arXiv2013

Wind-Driven Evolution of White Dwarf Binaries to Type Ia Supernovae

In the single degenerate scenario for the progenitors of type Ia supernovae (SNe Ia), a white dwarf rapidly accretes hydrogen- or helium-rich material from its companion star, and appears as a supersoft X-ray source. This picture has been challenged by the properties of the supersoft X-ray sources with very low-mass companions and the observations of several nearby SNe Ia. It has been pointed out that, the X-ray radiation or the wind from the accreting white dwarf can excite wind or strip mass from the companion star, thus significantly influence the mass transfer processes. In this paper we perform detailed calculations of the wind-driven evolution of white dwarf binaries. We present the parameter space for the possible SN Ia progenitors, and for the surviving companions after the SNe. The results show that the ex-companion stars of SNe Ia have characteristics more compatible with the observations, compared to those in the traditional single degenerate scenario.

astro-ph.HE↗