Қазақ ұлттық қыздар педагогикалық университеті / Казахский национальный женский педагогический университет

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Thin accretion-disc transfer functions in the q-metric spacetime: quadrupolar lensing signatures
(Cornell University, 2026-09-07)
Saken Toktarbay
;
Manas Khassanov
;
Aray Muratkhan
;
Zhantay Muratkhan
;
Aliya Taukenova
We study geometrically thin equatorial disc images in the static, axisymmetric q-metric spacetime using backward ray tracing. The Schwarzschild solution is recovered at $q=0$; for the nonzero deformations considered here, $r=2M$ is a curvature singularity rather than an event horizon. For a distant nearly face-on observer, we construct the first three equatorial transfer functions $r_m(b;q)$. In the {Schwarzschild} limit, the resolved third-crossing interval contains the critical impact parameter $b=3\sqrt{3}M$. As $q$ increases from $-0.3$ to $0.3$, the branch center shifts from $b_{3,c}/M\simeq3.716$ to $6.702$. In units of the physical monopole mass $\mathcal M=(1+q)M$, it instead decreases from $b_{3,c}/\mathcal M\simeq5.309$ to $5.156$. Much of the displacement in metric-parameter units therefore reflects the changing monopole scale. At fixed $\mathcal M$, the inclined first-intersection maps show that the contour dimensions increase with $q$, with larger relative changes near the inner disc. A prescribed power-law emissivity and relativistic frequency-shift weighting yield direct images whose integrated flux differs from the Schwarzschild value by at most $2.4\%$. Between the endpoint models, the horizontal median-flux position increases by $8.8\%$ and the interquartile width by $14.5\%$. Within this emission prescription, the residual deformation dependence appears mainly as a displacement and broadening of the brightness distribution. Higher-order radiative contributions are not included.
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Gravitational field of slightly deformed naked singularities
(Springer Science+Business Media, 2022-04-01)
Saken Toktarbay
;
Hernando Quevedo
;
Medeu Abishev
;
Aray Muratkhan
Abstract We derive a particular approximate solution of Einstein equations, describing the gravitational field of a mass distribution that slightly deviates from spherical symmetry. The deviation is described by means of a quadrupole parameter that is responsible for the appearance of a curvature singularity, which is not covered by a horizon. We investigate the motion of test particles in the gravitational field of this naked singularity and show that the quadrupole parameter affects the properties of Schwarzschild trajectories. By investigating radial geodesics, we find that no effects of repulsive gravity are present. We interpreted this result as indicating that repulsive gravity is non-linear effect.
Цитирования (OpenAlex) 12Цитирования (OpenCitations) 9
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A shadows from the static black hole mimickers
(Al-Farabi Kazakh National University, 2023-01-10)
Aray Muratkhan
;
Ayazhan Orazymbet
;
Madina Zhakipova
;
M. Assylbek
;
Saken Toktarbay
In this work, we study shadows from the naked singularity spacetime. The most analytical solutions of black hole shadows only investigated the case that the geodesic equations for photons can separate variables. We review the spherical null naked singularity metric and this spherically symmetric naked singularity spacetime metric is the solution of Einstein equations with an anisotropic fluid source which has no photon sphere. We also review a static, axially-symmetric singular solution of the vacuum Einstein’s equations without an event horizon which is can be used to describe the exterior gravitational field of a mass distribution with quadrupole moment. Moreover, the corresponding spacetime is characterized by the presence of naked singularities. It is theoretically known that not only a black hole can cast shadow, but other compact objects such as naked singularities, gravastar or boson stars can also cast shadows. We present the analytical calculation of shadows for both naked singularities spacetime and compare with the shadow of Schwarzschild static black hole, we show that this can serve as a black hole mimicker. Keywords: compact object, naked singularity, shadow.
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Application of GBT theorem for Gravitational deflection of light by Compact Objects
(Al-Farabi Kazakh National University, 2023-03-13)
Nurzada Beissen
;
Daniya Utepova
;
Aray Muratkhan
;
Ayazhan Orazymbet
;
Manas Khassanov
One of the most renowned classical experiments that verifies the curved nature of space-time geometry is the bending of light. This phenomenon is extensively discussed in most textbooks on general relativity, with a clear and comprehensive explanation provided. In this study, we employ the material medium approach to determine the refractive index associated with the gravitational field of a compact object with a quadrupole moment. Our research presents a method for calculating the gravitational deflection angle for compact objects by utilizing the refractive index and the GBT theorem for an isotropic metric. This method is particularly important because it allows for the calculation of the deflection angle for both light and relativistic particles. The material medium approach enables us to consider the compact object's gravitational field as a medium with a refractive index. By applying this approach, we establish a relationship between the refractive index and the quadrupole moment of the compact object. We then utilize this relationship to calculate the deflection angle of light and relativistic particles.
Цитирования (OpenAlex) 6Цитирования (OpenCitations) 3
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ВНУТРЕННЯЯ СТРУКТУРА И ОБЩЕРЕЛЯТИВИСТСКИЕ РАСЧЕТЫ КОМПАКТНЫХ ОБЪЕКТОВ
(2024-05-26)
Nurzada Beissen
;
Aray Muratkhan
;
T. Kapar
;
K. Amanbayeva
;
Tursynbek Yernazarov
tInthis study, we examine dense compact objects, such as white dwarfs and neutron stars, through the lens of Einstein's theory of gravity. Our focus is on understanding these objects when they are not perfectly spherical, using a mathematical description fortheir gravitational fields. We consider the quadrupole moment as an additional parameter that explicitly enters the equilibrium equations and the geometry of spacetime. In fact, most studies of equilibrium conditions in relativistic astrophysics are limited to the case of spherically symmetric sources. We construct approximate interior and exterior line elements, considering the quadrupole moment up to the first order, to describe static deformed compact objects. We pay particular attention to the interiors of slightly deformed compact objects, applying a specific formula known as the equation of state (EoS). This critical component enables us to understand how these stars balance the force of their own gravity with internal pressure. The EoS is pivotal in determining how matter behaves under the extreme conditions of density and pressure found within these compact objects. В исследовании мы рассматриваем плотные компактные объекты, такие как белые карлики и нейтронные звезды, через призму теории гравитации Эйнштейна. Наша цель –понять эти объекты, когда они не являются идеально сферическими, используя математическое описание их гравитационных полей. Мы учитываем квадрупольный момент как дополнительный параметр, который явно входит в уравнения равновесия и геометрию пространства-времени. Фактически, большинство исследований условий равновесия в релятивистской астрофизике ограничивается случаем сферически симметричных источников. Мы строим приблизительные внутренние и внешние элементы линии, учитывая квадрупольный момент до первого порядка, чтобы описать статически деформированные компактные объекты. Мы уделяем особоевнимание внутренностям слегка деформированных компактных объектов, применяя определенную формулу, известную как уравнение состояния (EoS). Этот критический компонент позволяет нам понять, как эти звезды уравновешивают силу собственной гравитации с внутренним давлением. EoS имеет решающее значение для определения поведения материи в экстремальных условиях плотности и давления, которые встречаются в этих компактных объектах. Бұл жұмыста, Эйнштейннің гравитация теориясы негізінде ақ ергежейлі және нейтрондық жұлдыздар сияқты тығыз жинақы нысандарды қарастырамыз. Біздің мақсатымыз -бұл объектілердіңгравитациялық өрістерінің математикалық сипаттамасын пайдалана отырып, олар сфералық симметриялы болмаған жағдайда олардың физикасын түсіну. Тепе-теңдік теңдеулері мен кеңістік-уақыт геометриясына нақты енгізілген қосымша параметр ретінде квадрупольдік моментті ескереміз. Шын мәнінде, релятивистік астрофизикадағы тепе-теңдік жағдайларын зерттеудің көпшілігі сфералық симметриялы көздермен шектеледі. Статикалық деформацияланған ықшам нысандарды сипаттау үшін бірінші ретке дейінгі квадрупольдік моментті ескере отырып, жуықталған ішкі және сыртқы сызық элементтерін пайдаланамыз. Күй теңдеуілері үшін (КТ) арнайы формуланы қолдану арқылы мардымсыз деформацияланған ықшам нысандардың ішкі құрылымына назар аударамыз. Бұл маңызды компонент жұлдыздардың өздерінің гравитациялық тартылыс күшін ішкі қысыммен қалай теңестіретінін түсінуге мүмкіндік береді. КТ осы ықшам нысандарда кездесетін тығыздық пен қысымныңтөтенше жағдайларындағы материяның әрекетін анықтау үшін өте маңызды.
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Analytical constraints on generalized β -velocity laws in X-ray-illuminated HMXBs
(Oxford University Press, 2026-03-20)
Saken Toktarbay
;
Aray Muratkhan
;
N. Myrzakulov
;
Zhantay Muratkhan
ABSTRACT We derive analytic constraints on the parameters of the generalized $\beta$-velocity law used to describe radiation-driven winds from OB (O- and B-type) supergiants in wind-fed X-ray binaries. Starting from the radial equation of motion with Castor–Abbott–Klein (CAK) line driving, gas pressure, and X-ray irradiation, we perform an asymptotic analysis of the near-base region and show that a monotonic CAK-type acceleration requires the exponent of the velocity law to satisfy a robust lower bound $\beta _{\min }=1/2$. A separate condition follows from requiring the $\beta$-law to connect smoothly to the subsonic layers: the wind speed at the stellar surface must be at least comparable to the isothermal sound speed, which yields a conservative upper limit on the onset parameter, $b \lesssim 1-\left(a_{\rm s}/v_\infty \right)^{1/\beta }$,and implies $b_{\max } \approx 0.95$–0.99 for typical OB-star parameters. We include the effects of X-ray photoionization and attenuation in an approximate way by introducing an effective force-multiplier slope $\alpha _{\rm eff}$ and an optical-depth parameter controlling the weakening of X-ray inhibition. A scaling analysis shows that strong irradiation favours larger $\beta$ and can lead to the loss of monotonic acceleration, providing an effective system-dependent upper limit on the acceleration index. To assess the consistency of these bounds, we integrate a simplified momentum equation and fit the resulting accelerating solutions with a generalized $\beta$-law. The best-fitting pairs $(b,\beta)$ lie within the analytically allowed domain and occupy the range $\beta \approx 0.6$–1.2, in good agreement with empirical determinations for several persistent high-mass X-ray binaries. Our results provide physically motivated constraints on velocity-law parameters that can guide wind modelling and the interpretation of spectroscopic diagnostics in irradiated massive-star winds.
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COMPARATIVE ANALYSIS OF X-RAY LUMINOSITY OF PERSISTENT AND TRANSIENT HIGH-MASS X-RAY BINARIES
(2026-03-29)
Zhantay Muratkhan
;
Manas Khassanov
;
Aray Muratkhan
;
Aliya Taukenova
;
A. Sadu
High-mass X-ray binaries (HMXBs) are commonly divided into persistent sources, which emit X-rays steadily over long periods, and transient sources, which remain mostly in a quiescent state and exhibit episodic X-ray outbursts. The aim of this work is to statistically compare the X-ray luminosity properties of these two classes, focusing on the maximum luminosity and the luminosity variability range . For this purpose, catalog data for Galactic HMXB pulsars were used, including 18 persistent and 64 transient systems. The distributions of and were analyzed using histograms, box plots, cumulative distribution functions (CDFs), and the non-parametric Mann–Whitney test. It is shown that both classes reach similar values of on the order of – erg/s), with no statistically significant difference between their distributions. However, transient systems exhibit a much wider luminosity variability range, reaching increases of 4–5 orders of magnitude (up to ), whereas persistent sources typically show lower variability. This difference is statistically confirmed, with transients demonstrating significantly higher variability p ≈ 0.05). Thus, the main distinction between persistent and transient HMXBs lies not in their peak X-ray luminosity, but in their accretion regime. In persistent systems, the compact object continuously accretes matter from a relatively stable stellar wind of an OB supergiant, resulting in steady X-ray emission. In contrast, transient systems are characterized by intermittent accretion (for example, episodic mass capture from a Be-star circumstellar disc), which leads to their extreme luminosity variability.
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Correlation analysis of the wind acceleration parameter in high-mass X-ray binaries
(Al-Farabi Kazakh National University, 2026-06-19)
Zhantay Muratkhan
;
Saken Toktarbay
;
Aray Muratkhan
;
Aliya Taukenova
;
Nadeem Azhar
This work presents a correlation analysis of the wind acceleration parameter β in high-mass X-ray binaries (HMXBs). The aim of the study is to determine how β depends on the geometric and dynamical characteristics of the system, primarily on the ratio of the orbital radius to the stellar radius, a⁄R_* and on the terminal wind velocity v_∞. For this purpose, published values of R_*, a and v_∞ together with measured wind velocities in the vicinity of the neutron star, were used. Based on these data, the parameters of the β-velocity law were determined numerically. The resulting β values were then approximated using a linear regression, β≈k a⁄R_* +c, yielding a simple empirical relation. The results show that the linear correlation between β and the orbital-to-stellar radius ratio is weak (with a Pearson correlation coefficient r ≈ 0.22) and is accompanied by substantial scatter, indicating the influence of additional physical factors. The linear regression yields a small positive slope (k ≈ 0.14), which suggests only a weak tendency for β to increase with the orbital ratio. Because of the small sample size, this trend should be regarded as tentative. The proposed linear model allows β to be estimated without detailed spectroscopic analysis and may be useful as a rough empirical indicator of wind-accretion properties in HMXBs. The originality of this study lies in providing a simple empirical first-order assessment of the β parameter in HMXBs based on observed orbital and wind properties in systems where detailed spectroscopic constraints are limited. Key words: high-mass X-ray binaries (HMXBs), β-law (β-velocity profile), wind velocity profile, terminal wind velocity, orbital ratio a⁄R_* , correlation analysis.
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Vertical epicyclic stability and dissipative settling in a weakly deformed q-metric spacetime
(L. N. Gumilyov Eurasian National University, 2026-09-30)
Ayazhan Orazymbet
;
Aray Muratkhan
;
Aliya Taukenova
;
A. Dalelkhankyzy
We investigate the motion of massive test particles close to the equatorial plane of a weakly deformed q-metric spacetime. Working to first order in the dimensionless quadrupole parameter q, we derive the orbital angular velocity and the vertical epicyclic frequency for equatorial circular orbits while keeping the physical monopole mass fixed. The Schwarzschild limit is recovered at q = 0, whereas a nonzero quadrupole removes the degeneracy between the vertical and azimuthal frequencies already at O(q). A small phenomenological damping term is then introduced into the linearized vertical equation to describe the gradual approach of a perturbed orbit toward the equatorial plane. In the conservative case, the particle continues to oscillate about this plane without any decrease in amplitude. With damping, the amplitude decays exponentially. The quadrupolar deformation changes the vertical oscillation frequency and, consequently, the number of cycles completed before a specified settling threshold is reached. It does not, however, set the decay timescale, which follows from the adopted damping prescription. Since the coordinate-time damping coefficient is kept fixed in our numerical examples, the trajectories share the same exponential envelope but oscillate at different frequencies. The comparison with the exact q-metric also provides a direct check of the firstorder approximation. Over the sampled domain |q| ≤ 0.1 and 6 ≤ r/M ≤ 20, the relative error in the vertical frequency remains below 0.34%, while the corresponding frequency ratio is reproduced to better than 0.10%. These results show explicitly how the quadrupolar geometry modifies vertical orbital dynamics within a model in which dissipative settling is introduced independently.

Қазақ ұлттық қыздар педагогикалық университеті / Казахский национальный женский педагогический университет

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