arXiv subjects

Long Jiang

Publications and source records attributed to Long Jiang.

30 records · Page 2Linked to original sources

arXiv2021

Influence of irradiation-driven winds on the evolution of intermediate-mass black hole X-ray binaries

In young dense clusters, an intermediate-mass black hole (IMBH) may get a companion star via exchange encounters or tidal capture, and then evolves toward IMBH X-ray binary by the Roche lobe overflow. It is generally thought that IMBH X-ray binaries are potential ultra-luminous X-ray sources (ULXs), hence their evolution is very significant. However, the irradiation-driven winds by the strong X-ray flux from the accretion disks around the IMBHs play an important role in determining the evolution of IMBH X-ray binaries, and should be considered in the detailed binary evolution simulation. Employing the models with the MESA code, we focus on the influence of irradiation-driven winds on the evolution of IMBH X-ray binaries. Our simulations indicate that a high wind-driving efficiency ($f=0.01$ for $Z=0.02$, and $f=0.002$ for $Z=0.001$) substantially shorten the duration in the ULX stage of IMBH X-ray binaries with an intermediate-mass ($5~M_{\odot}$) donor star. However, this effect can be ignored for high-mass ($10~M_{\odot}$) donor stars. The irradiation effect ($f=0.01$ or $0.002$) markedly shrink the initial parameter space of IMBH binaries evolving toward ULXs with high luminosity ($L_{\rm X}>10^{40}~\rm erg\,s^{-1}$) and hyperluminous X-ray sources in the donor-star mass versus orbital period diagram. Furthermore, the irradiation effect results in an efficient angular momentum loss, yielding to IMBH X-ray binaries with relatively close orbits. In our simulated parameter space, about 1\% of IMBH binaries would evolve toward compact X-ray sources owing to short initial orbital periods, some of which might be detected as low-frequency gravitational wave sources.

astro-ph.HE↗

arXiv2021

On the progenitors of AM CVn stars as LISA sources: the evolved donor star channel

The space gravitational wave (GW) detector Laser Interferometer Space Antenna (LISA) that was planed to launch in the early 2030s is to detect the low-frequency GW signals in the Galaxy. AM CVn stars were generally thought to be important low-frequency GW sources. Employing the MESA code, in this work we calculate the evolution of a great number of binary systems consisting of a white dwarf (WD) and a main sequence (MS) star, and diagnose whether their descendants-AM CVn stars can be visible by the LISA. The simulated results show that the progenitors of these LISA sources within a distance of 1 kpc are WD-MS binaries with a donor star of $1.0-1.4~M_\odot$ (for initial WD mass of $0.5~M_\odot$) or $1.0-2.0~M_\odot$ (for initial WD mass of $0.7~M_\odot$), and an initial orbital period slightly smaller than the bifurcation period. Our simulations also indicate ten verification AM CVn sources can be reproduced by the standard magnetic braking model, and are potential LISA sources. Based on the birthrate of AM CVns simulated by the population synthesis, the birthrate of AM CVn-LISA sources evolving from the evolved donor star channel within a distance of 1 kpc can be estimated to be $(0.6-1.4)\times10^{-6}~\rm yr^{-1}$, and the predicted number of AM CVn-LISA sources is about $340-810$. Therefore, the evolved donor star channel play an important role in forming AM CVn-LISA sources in the Galaxy.

astro-ph.SR↗

arXiv2020

A Kaczmarz Method with Simple Random Sampling for Solving Large Linear Systems

The Kaczmarz method is a popular iterative scheme for solving large-scale linear systems. The randomized Kaczmarz method (RK) greatly improves the convergence rate of the Kaczmarz method, by using the rows of the coefficient matrix in random order rather than in their given order. An obvious disadvantage of the randomized Kaczmarz method is its probability criterion for selecting the active or working rows in the coefficient matrix. In [{\sc Z.Z. Bai, W. Wu}, {\em On greedy randomized Kaczmarz method for solving large sparse linear systems}, SIAM Journal on Scientific Computing, 2018, 40: A592--A606], the authors proposed a greedy randomized Kaczmarz method (GRK). However, this method may suffer from heavily computational cost when the size of the matrix is large, and the overhead will be prohibitively large for big data problems. The contribution of this work is as follows. First, from the probability significance point of view, we present a partially randomized Kaczmarz method, which can reduce the computational overhead needed in greedy randomized Kaczmarz method. Second, based on Chebyshev's law of large numbers and Z-test, we apply a simple sampling approach to the partially randomized Kaczmarz method. The convergence of the proposed method is established. Third, we apply the new strategy to the ridge regression problem, and propose a partially randomized Kaczmarz method with simple random sampling for ridge regression. Numerical experiments demonstrate the superiority of the new algorithms over many state-of-the-art randomized Kaczmarz methods for large linear systems problems and ridge regression problems.

math.NA↗

arXiv2019

A strange star scenario for the formation of isolated millisecond pulsars

According to the recycling model, neutron stars in low-mass X-ray binaries were spun up to millisecond pulsars (MSPs), which indicates that all MSPs in the Galactic plane ought to be harbored in binaries. However, about $20\%$ Galactic field MSPs are found to be solitary. To interpret this problem, we assume that the accreting neutron star in binaries may collapse and become a strange star when it reaches some critical mass limit. Mass loss and a weak kick induced by asymmetric collapse during the phase transition (PT) from neutron star to strange star can result in isolated MSPs. In this work, we use a population-synthesis code to examine the PT model. The simulated results show that a kick velocity of $\sim60~{\rm km~s}^{-1}$ can produce $\sim6\times10^3$ isolated MSPs and birth rate of $\sim6.6\times10^{-7} {\rm ~yr}^{-1}$ in the Galaxy, which is approximately in agreement with predictions from observations. For the purpose of comparisons with future observation, we also give the mass distributions of radio and X-ray binary MSPs, along with the delay time distribution.

astro-ph.HE↗

arXiv2018

A strange dwarf scenario for the formation of the peculiar double white dwarf binary SDSS J125733.63+542850.5

The Hubble Space Telescope observation of the double white dwarf (WD) binary SDSS J125733.63$+$542850.5 reveal that the massive WD has a surface gravity log$g_1\sim8.7$ (which implies a mass of $M_1\sim1.06~{\rm M_\odot}$) and an effective temperature $T_1\sim13000$ K, while the effective temperature of the low-mass WD ($M_2<0.24$ {\rm M$_\odot$}) is $T_2\sim6400K$. Therefore, the massive and the low-mass WDs have a cooling age $τ_1\sim1$ {\rm Gyr} and $τ_2\geq5$ {\rm Gyr}, respectively. This is in contradiction with traditional binary evolution theory. In this Letter, we propose a strange dwarf scenario to explain the formation of this double WD binary. We assume that the massive WD is a strange dwarf originating from a phase transition in a $\sim1.1$ M$_\odot$ WD, which has experienced accretion and spin-down processes. Its high effective temperature could arise from the heating process during the phase transition. Our simulations suggest that the progenitor of SDSS J125733.63$+$542850.5 can be a binary system consisting of a $0.65~\rm M_{\odot}$ WD and a $1.5~\rm M_{\odot}$ main sequence star in a 1.492 day orbit. Especially, the secondary star (i.e., the progenitor of the low mass WD) is likely to have an ultra-low metallicity of $Z=0.0001$.

astro-ph.HE↗

arXiv2017

A Circumbinary Disk Scenario For The Negative Orbital-Period Derivative Of The Ultracompact X-ray Binary 4u1820-303

It is generally thought that an ultracompact X-ray binary is composed with a neutron star and a helium white dwarf donor star. As one of the most compact binaries, 4U 1820-303 in globular cluster NGC 6624 was predicted an orbital-period derivative at a rate of $\dot{P}/P\sim1.1\times10^{-7}$ ${\rm yr^{-1}}$ if the mass transfer is fully driven by gravitational radiation. However, the recent analysis of the 16 ${\rm yr}$ data from \textit{Rossi X-ray Timing Explorer} and other historical records yielded a negative orbital-period derivative in the past $35$ yr. In this work, we propose an evolutionary circumbinary (CB) disk model to account for this anomalous orbital-period derivative. 4U 1820-30 was known to undergo superbust events caused by runaway thermal nuclear burning on the neutron star. We assume that for a small fraction of the superbursts, part of the ejected material may form a CB disk around the binary. If the recurrence time of such superbursts is $\sim10,000$ yr and $\sim10$% of the ejected mass feeds a CB disk, the abrupt angular-momentum loss causes a temporary orbital shrink, and the donor's radius and its Roche-lobe radius do not keep in step. Driven by mass transfer and angular-momentum loss, the binary would adjust its orbital parameters to recover a new stable stage. Based on the theoretical analysis and numerical simulation, we find that the required feed mass at the CB disk is approximately $\sim 10^{-8}$ ${\rm M_{\odot}}$.

astro-ph.HE↗

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↗

arXiv2014

$L^p$ solutions of finite and infinite time interval BSDEs with non-Lipschitz coefficients

In this paper, we are interested in solving multidimensional backward stochastic differential equations (BSDEs) in $L^p\ (p>1)$ under weaker assumptions on the coefficients, considering both a finite and an infinite time interval. We establish a general existence and uniqueness result of solutions in $L^p\ (p>1)$ to finite and infinite time interval BSDEs with non-Lipschitz coefficients, which includes the corresponding results in \citet{Par90}, \citet{Mao95}, \citet{Chen97}, \citet{Cons01}, \citet{Wang03}, \citet{Chen00} and \citet{Wang09} as its particular cases.

math.PR↗

arXiv2014

$L^p$ solutions of BSDEs with a new kind of non-Lipschitz coefficients

In this paper, we are interested in solving multidimensional backward stochastic differential equations (BSDEs) with a new kind of non-Lipschitz coefficients. We establish an existence and uniqueness result of solutions in $L^p\ (p>1)$, which includes some known results as its particular cases.

math.PR↗

arXiv2013

On the formation of the peculiar low-mass X-ray binary IGR J17480$-$2446 in Terzan 5

IGR J17480$-$2446 is an accreting X-ray pulsar in a low-mass X-ray binary harbored in the Galactic globular cluster Terzan 5. Compared with other accreting millisecond pulsars, IGR J17480$-$2446 is peculiar in its low spin frequency (11 Hz), which suggests that it might be a mildly recycled neutron star at the very early phase of mass transfer. However, this model seems to be in contrast with the low field strength deduced from the kiloHertz quasi-periodic oscillations observed in IGR J17480$-$2446. Here we suggest an alternative interpretation, assuming that the current binary system was formed during an exchange encounter either between a binary (which contains a recycled neutron star) and the current donor, or between a binary and an isolated, recycled neutron star. In the resulting binary, the spin axis of the neutron star could be parallel or anti-parallel with the orbital axis. In the later case, the abnormally low frequency of IGR J17480$-$2446 may result from the spin-down to spin-up evolution of the neutron star. We also briefly discuss the possible observational implications of the pulsar in this scenario.

astro-ph.HE↗

arXiv2011

User-level sentiment analysis incorporating social networks

We show that information about social relationships can be used to improve user-level sentiment analysis. The main motivation behind our approach is that users that are somehow "connected" may be more likely to hold similar opinions; therefore, relationship information can complement what we can extract about a user's viewpoints from their utterances. Employing Twitter as a source for our experimental data, and working within a semi-supervised framework, we propose models that are induced either from the Twitter follower/followee network or from the network in Twitter formed by users referring to each other using "@" mentions. Our transductive learning results reveal that incorporating social-network information can indeed lead to statistically significant sentiment-classification improvements over the performance of an approach based on Support Vector Machines having access only to textual features.

cs.CL↗

arXiv2008

Convexity, translation invariance and subadditivity for $g$-expectations and related risk measures

Under the continuous assumption on the generator $g$, Briand et al. [Electron. Comm. Probab. 5 (2000) 101--117] showed some connections between $g$ and the conditional $g$-expectation $({\mathcal{E}}_g[\cdot|{\mathcal{F}}_t])_{t\in[0,T]}$ and Rosazza Gianin [Insurance: Math. Econ. 39 (2006) 19--34] showed some connections between $g$ and the corresponding dynamic risk measure $(ρ^g_t)_{t\in[0,T]}$. In this paper we prove that, without the additional continuous assumption on $g$, a $g$-expectation ${\mathcal{E}}_g$ satisfies translation invariance if and only if $g$ is independent of $y$, and ${\mathcal{E}}_g$ satisfies convexity (resp. subadditivity) if and only if $g$ is independent of $y$ and $g$ is convex (resp. subadditive) with respect to $z$. By these conclusions we deduce that the static risk measure $ρ^g$ induced by a $g$-expectation ${\mathcal{E}}_g$ is a convex (resp. coherent) risk measure if and only if $g$ is independent of $y$ and $g$ is convex (resp. sublinear) with respect to $z$. Our results extend the results in Briand et al. [Electron. Comm. Probab. 5 (2000) 101--117] and Rosazza Gianin [Insurance: Math. Econ. 39 (2006) 19--34] on these subjects.

math.PR↗