Astrophysics and Space Science最新文献

The well-observed type IIP SN 2024bch with the short plateau is shown to be an outcome of the red supergiant explosion with the presupernova mass of (14-15) (M_{odot }), the explosion energy of (2times 10^{51}) erg, and presupernova radius of 1250 (R_{odot }). The early gamma-ray escape demonstrated by the radioactive tail is due to the large ⁵⁶Ni extension up to 7400 km s⁻¹. The early-time spectral evolution indicates the presence of the circumstellar dense confined envelope with the mass of (0.003-0.006) (M_{odot }) within (6times 10^{14}) cm. The deceleration of the outermost ejecta implies the wind with the mass-loss rate of ≈ 6(times 10^{-4}) (M_{odot }) yr⁻¹. The inferred mass-loss rate is by one-two order larger compared to most of type IIP supernovae, but comparable to the wind of type IIL SN 1998S. The asymmetry of the broad H(alpha ) component on day 144 powered by the circumstellar interaction is the outcome of the Thomson scattering and absorption in the Paschen continuum in the unshocked ejecta.

We present the rotation curves of seven dwarf galaxies from the Local Volume Hi Survey (LVHIS) to investigate their Hi gas kinematics and mass distribution. The LVHIS Hi data cubes, with a spatial resolution of 40–50″ and a spectral resolution of (sim 4~mathrm{km},mathrm{s}^{-1}), allow for a detailed analysis of gas kinematics and the relative contributions of baryons and dark matter. Using a Bayesian–based profile decomposition method, we identify kinematic complexities in the gas, particularly in the inner regions, which may arise from observational beam smearing or stellar feedback processes. Through 2D tilted–ring analysis, we derive rotation curves that exhibit solid-body rotation in the inner regions, transitioning to flat or gradually rising curves in the outer parts. An asymmetric drift correction applied to the rotation curves shows minimal impact, attributed to the low Hi velocity dispersion and gas surface densities in the galaxies’ outer regions. Disk—halo decomposition using the Cold Dark Matter NFW and pseudo-isothermal halo models is limited by the coarse spatial resolution of the LVHIS Hi data and the absence of high–quality optical and infrared observations, which hinders a clear distinction between the models. Nonetheless, this study complements our understanding of the overall rotation curve shapes and Hi gas kinematics of galaxies in the local Universe.

Convection in the innermost shells of massive stars plays an important role in initiating core-collapse supernovae. When these convective motions reach the supernova shock, they create extra turbulence, which helps energize the explosion. In our earlier work, we studied the effect of rotation on the hydrodynamic evolution of convective vortices in collapsing stars. This study focuses on how rotation influences the entropy perturbations, which naturally form in turbulent convection. As these perturbations are carried inward with the collapsing star, they generate both vorticity and sound waves. Using linear perturbation theory, we model entropy waves as small disturbances on top of a steady background flow. Our results show that stellar rotation has little effect on the evolution of entropy perturbations during collapse, prior to encountering the supernova shock. This outcome is consistent with our earlier findings on the limited influence of rotation in the accretion of convective eddies.

A valuable probe for examining relativistic gravity, star stricture, and the dynamical development of near binary systems is the apsidal motion of a non-synchronous binary pulsar. In this study, we examine the combined effects of tidal interaction, star oblateness, and general relativity on the apsidal motion of three binary pulsars: J0621+1002, J0737-3039A/B, and 1913+16. Tidal effects and their role in orbital and spin evolution were described by numerical integrations using Zahn’s tidal equations (Astron. Astrophys. 57:383–394, 1977, Astron. Astrophys. 220:112–116, 1989). We calculated the orbital circularization and tidal synchronization timescales for each system. The simulated results show a clear trends of decreasing of both the semi-axis and eccentricity, while increasing the spin rate. In addition, the tidal effects play only a minor role in orbital decay compared with energy loss due to gravitational wave emission. Both the obtained apsidal motion constants [(ksimeq 0.1)] and the derived tidal friction periods, which vary from a few hours to several days, correspond well with theoretical estimates. This is demonstrated in the compact system PSR1913+16, where gravity radiation causes the orbital period to decrease by approximately 76.5 μs/yr. While the wider system J0621+1002 displays minor orbital change over timescale exceeding 10¹⁰ yrs, the double pulsar J0737-3039A/B exhibits faster orbital evolution, with synchronization occurring in about 8.4(times 10{^{3}}) yrs. The results demonstrate the significance of relativistic effects in neutron star binaries and the necessity of incorporating gravitational wave terms in long-term orbital evolution.

This research examines the variations of the relativistic electron flux (REF) with E > 0.8 MeV and > 2 MeV at geostationary orbit (GEO) and in outer radiation belts (ORB) selected events of high-intensity long-duration continuous AE activity (HILDCAA) during 2015 to 2017. We have utilized the solar wind plasma data and geomagnetic storm indices, source and seed electron flux, chorus wave spectrograms, and ULF indices. We found strong linear correlation between the maximum of AE (AL) and max REF, and between the peaks solar wind speed (V_max) and max Log REF. The E > 0.8 MeV REF increases before the E > 2.0 MeV REF. Then they concurrently changed with the increasing rate of the E > 2.0 MeV REF is faster than that of the E > 0.8 MeV REF. The Alfvénicity (i.e., the extent to which fluctuations follow the Alfvén wave characteristics), with the southward interplanetary magnetic field of the Alfvén waves is essential for the substorm occurrence. The REF enhancements at GEO are categorized into nominal, high, and very high levels. The conditions of very high REF are 1690 ≤ AE_max ≤ 2178 nT and 742 ≤ V_max ≤ 860 km/s. The large ULF waves are found in the high and very high REF and often appear in the high-Alfvénic events. The Chorus wave activity persists in conjunction with the injection of source and seed electrons. Nominal REF occurs in the moderate ULF and the highest REF was around L = 4–5 without loss of REF in the ORB. The prominent Chorus and ULF waves recurrently appear in some consecutive HILDCAA events that sequentially and synergistically enhance the REF to very high levels. Near L = 4, the REF was locally enhanced by Chorus wave throughout the HILDCAA and recovery phase. The consecutive recurrent Chorus relates to the loss of REF in the range of L = 4–6. Events with no clear Chorus in the ORB can possess high and very high REF at GEO and the loss of REF is at L = 4–5 during the Equinoctial times. Moreover, REF shows semiannual variation, with maxima fluxes near the equinoxes.

The goal of this paper is to obtain an approximate solution of the restricted three-body problem in the case of small perturbations in the vicinity of, but not in exact resonance. In this paper, we study the restricted three-body problem known as planetary type (i.e., when the eccentricity of the test particle is small). A method of linearizing the equation of motion close to (but not in) resonance is proposed under the assumption of small perturbations. In other words, we study orbits when the resonant argument circles the resonance. In the practically interesting case of resonant perturbations we can restrict our study to a perturbation with a single frequency with the largest amplitude, and reduce the problem to the Mathieu equation. The model qualitatively describes the behavior of the perturbation in the vicinity of the resonance. It can be used to estimate the exact position of the resonance and the boundaries between neighboring resonances.

Arrays of precisely-timed millisecond pulsars are used to search for gravitational waves with periods of months to decades. Gravitational waves affect the path of radio pulses propagating from a pulsar to Earth, causing the arrival times of those pulses to deviate from expectations based on the physical characteristics of the pulsar system. By correlating these timing residuals in a pulsar timing array (PTA), one can search for a statistically isotropic background of gravitational waves by revealing evidence for a distinctive pattern predicted by General Relativity, known as the Hellings & Downs curve. On June 29 2023, five regional PTA collaborations announced the first evidence for GWs at light-year wavelengths, predicated on support for this correlation pattern with statistical significances ranging from (sim !2-4sigma ). The amplitude and shape of the recovered GW spectrum has also allowed many investigations of the expected source characteristics, ranging from a cosmic population of supermassive binary black holes to numerous processes in the early Universe. In the future, we expect to resolve signals from individual binary systems of supermassive black holes, and probe fundamental assumptions about the background, including its polarization, anisotropy, Gaussianity, and stationarity, all of which will aid efforts to discriminate its origin. In tandem with new facilities like DSA-2000 and the SKA, fueling further observations by regional PTAs and the International Pulsar Timing Array, PTAs have extraordinary potential to be engines of nanohertz GW discovery.

In this work, we analytically derive the caustic equation for a general (N)-point gravitational lens using methods from algebraic geometry and complex function theory. Based on this equation, we construct the full pre-image of the caustic in the lens plane. This pre-image includes not only the critical curve but also additional closed curves that partition the lens plane into regions mapped to the interior and exterior of the caustic in the source plane. These regions define topological domains within which the number of lensed images remains constant. Notably, when the source moves within a region that does not intersect the caustic, its corresponding images remain confined to specific regions of the lens plane. The effectiveness of the proposed approach is demonstrated using the example of a general binary gravitational lens system.

We present a physically motivated extension of the FP for elliptical galaxies, derived from the scalar virial theorem and calibrated using observational data. Starting from the basic equilibrium condition, we incorporate key physical parameters that govern galaxy structure and dynamics, namely stellar mass-to-light ratio, central dark matter fraction, and structural non-homology as traced by the Sérsic profile. The resulting model retains the original dependencies on velocity dispersion and surface brightness, but introduces physically interpretable corrections that significantly improve the fit to real data. Using a large galaxy sample, we demonstrate that this extended FP achieves a higher level of accuracy than the classical form, with all parameters showing strong statistical significance. Our results indicate that the observed FP can be understood as an empirical refinement of the virial prediction, once variations in stellar populations, dark matter content, and internal structure are taken into account. This work provides a unified framework that bridges theoretical expectations with observed scaling relations in elliptical systems.

Classical attempts to construct a galaxy model, in a stationary and axisymmetric situation, consist of giving a gravitational field and injecting it into the collisionless Boltzmann equation to deduce the solution distribution function f. We will do exactly the opposite, by assimilating the galaxy to a self-gravitating point-mass system. The velocity distribution function is then the solution of an integrodifferential equation. Taking into account the Newtonian character of the potential, we can replace it with the system consisting of the Vlasov equation, written in terms of residual velocity, and the Poisson equation. We then give (ln(f)) the form of a polynomial of degree 2, such that one of the axes of the velocity ellipsoid points towards the center of the system. This single constraint gives the evolution of the axes in space, these being equal to the center of the galaxy (Maxwell-Boltzmann distribution). Moving away from the center, the axis pointing in this direction remains constant while the transverse axes tend to zero at infinity. We then construct the macroscopic velocity field by excluding any vortex structure. This field then tends towards a solid body rotation at the center. The velocity tends towards a remote plateau, which is then consistent with the observational data.