Astrophysics and Space Science最新文献

We have carried out a detailed study of the Gamma-Ray Burst (GRB) photospheric emission model predicting a quasi-blackbody spectrum slightly broader than a Planck function. This model was suggested within the relativistic fireball dynamics for interpreting a still not well understood thermal component in the GRB prompt emission, recently observed by the GBM (Gamma-ray Burst Monitor) on board the Fermi space telescope. We propose a Monte Carlo (M C) code for elucidating the observed spectrum, the outflow dynamics and its geometry for a basic and a structured plasma jets whose parameters are implemented. The code involves a simulation part describing the photon propagation assuming an unpolarized, non-dissipative relativistic outflow and a data analysis part for exploring main photospheric emission properties such as the energy, arrival time and observed flux of the simulated seed photons and the photospheric radius. Computing the latter two observables by numerical integration, we obtained values very concordant with the M C simulated results. Fitting Band functions to the photon spectra generated by this method, we derived best-fit values of the photon indices matching well those featuring the observed spectra for most typical GRBs, but corresponding to fit functions inconciliable with blackbody spectral shapes. Various derived results are reported, compared to previous ones and discussed. They show to be very sensitive to the structure of the Lorentz factor that plays a crucial role in determining the presence and strength of geometrical effects. The latter manifest themselves by large broadenings of the simulated spectra featured by multiple peak energies consistently with GRB observations. They are assumed, with multiple Compton scattering, to produce bumps pointed out at very low photon energies. The interpretation of GRB observations is further performed via a Band spectral analysis using the RMFIT software. Finally, developments of this work are put into perspective.

In a recent series of papers, Leibowitz revealed two pacemaker frequencies associated with flares observed near the Sgr A* location: one for X-ray flares and the other for IR (infrared) flares. He proposed an astrophysical model to account for these two frequencies, involving a unique body orbiting the Sgr A* black hole (supposed nonrotating) close to its last stable circular orbit. In the framework of this model, the Roche lobe contacts the star’s surface near the periastrons, which generates matter pullouts. The resulting X events are then separated by time intervals that are close to integer multiples of the radial orbital frequency, which explains the X pacemaker. One revisits this X sequence orbiting-body interpretation but in a full general relativistic framework, which is more appropriate than the pseudo-Newtonian Paczyński-Wiita potential approach used by Leibowitz. One concludes that no main sequence (or giant) star can survive the tidal effects, whereas no pullout matter is possible for white dwarfs (or neutron stars), on the orbits compatible with the X pacemaker frequency, even if large eccentricities are allowed. This confirms the result obtained by Leibowitz (on the impossibility of a main sequence or usual compact star, since the only solution he found involves an “unusual internal structure star”) but (1) in the framework of full relativistic calculations and (2) extending the result to the eccentric case.

A comprehensive analysis of barred galaxies in triplet systems, drawn from the SDSS-based catalog of isolated galaxy triplets composed of 315 triplet systems (945 galaxy members) is presented. The primary objective for this study is to investigate the bar fraction ((f_{bar})) within these systems and explore its correlation with various intrinsic and extrinsic properties of the triplets. Our final sample, after excluding highly inclined and merging galaxies, comprises 427 galaxy members embedded in 232 triplet systems. The final sample reveals a bar fraction of 42(%) with a bar fraction that significantly increases in nearby systems (with smaller redshift) characterized by higher virial mass ((M_{vir})), lower radial velocities ((sigma )) among their members, and larger angular separations ((r_{p})) and harmonic projected distances ((r_{h})) between the triplet members. Additionally, it has been noticed that the large-scale structure (LSS) influences the bar fraction, with (f_{bar}) decreasing as the distance from the primary galaxy (G1) to the first neighborhood increases ((d_{NN})). Furthermore, (f_{bar}) decreases as tidal strength generated by the galaxies in the (LSS) ((Q_{LSS}))increases. These findings suggest that both the dynamical environment and the local interactions within triplet systems significantly impact the abundance of barred structures. This study provides valuable insights into the role of environmental factors in shaping galaxy morphology, particularly in systems with complex gravitational interactions.

Accurate real-time solar radio burst (SRB) detection is crucial for solar physics research and space weather forecasting. Currently, most studies on solar radio burst detection focus on single-category identification and simple discrimination of bursts. There are limited existing studies on multi-category detection. This paper proposes a real-time multi-category solar radio burst detection method to meet the requirements of real-time detection, detection accuracy, and classification accuracy in solar radio bursts. First, solar radio burst spectrums were collected from e-CALLISTO. The spectrums are labeled using LabelImg, and a dataset containing solar radio bursts of Type II, Type III, Type IIIs, Type IV, and Type V was established. Second, a full-dimensional dynamic convolution was introduced in the backbone module of the YOLOv8n model, enhancing the model’s feature extraction capability. Third, a multi-scale feature fusion network based on ConvNeXt was created to prevent feature information loss and optimize the loss function. The experimental results show that the proposed method achieves an average detection accuracy of 82.4% on the established solar radio burst dataset. Compared with the original YOLOv8n model, the accuracy increased by 3.5%. Additionally, the model operates at 140.9 frames per second, with each frame representing a spectrum of 15 minutes duration. Thus, the improved YOLOv8n model enhances the detection accuracy and speed of solar radio bursts, enabling automatic detection and localization of solar radio bursts of Type II, Type III, Type IIIs, Type IV, and Type V.

This study examines the possibility of starting the process of collapsing and forming stars from a fractional molecular cloud. Although the Verlinde’s approach is employed to derive the corresponding gravitational potential, the results are easily generalizable to other gravitational potential proposals for fractional systems. It is due to the fact that the different methods, despite the difference in the details of results, all obtain power forms for the potential in terms of radius. An essential result of this analysis is the derivation of the corresponding Jeans mass limit, which is a crucial parameter in understanding the formation of stars. The study shows that the Jeans mass of a cloud in fractional gravity is much smaller than the traditional value. In addition, the study also determines the burning temperature of the resulting star using the Gamow theory. This calculation provides insight into the complex processes that govern the evolution of these celestial bodies. Finally, the study briefly discusses the investigation of hydrostatic equilibrium, a crucial condition that ensures the stability of these fractional stars. It also addresses the corresponding Lane–Emden equation, which is pivotal in understanding this equilibrium.

By using the quadratic equation of state and the anisotropic energy-momentum tensor for compact stars in spherically symmetric spacetime in hydrostatic static equilibrium to solve Einstein’s field equation, we are able to create a new class of models for compact stars. We developed new solutions by solving the field equations for the distribution of matter using a well-known Buchdahl metric potential (Buchdahl in Phys. Rev. D 116:1027, 1959). The resulting anisotropic solutions exhibit good behavior and obey the energy conditions. By analyzing the TOV equation, we have confirmed the stability of the produced model, Harrison-Zeldovik-Novikov criterion, and the adiabatic index for the solution. The fulfillment of all these criteria makes this model to be utilized for the study of realistic compact objects. Also, we measured the masses and radii of star candidates like “4U 1820-30”, “PSR J1903+327”, “4U 1608-52”, “Vela X-1”, “PSR J1614-2230”, and “Cyg X-2” through this model and found these values compatible with observational values of corresponding stars. For each of the considered compact stars, we have obtained the approximate value of the moment of inertia via the obtained solution.

By considering the steady-state Novikov-Thorne model, we study thin accretion disk processes for rotating hairy black holes in the framework of the Horndeski gravity. We obtain the electromagnetic properties of accretion disk around such black holes and investigate the effects of the hair parameter (h) on them. We find that by decreasing the hair parameter from the Kerr limit, (hrightarrow 0), the radius of the innermost stable circular orbit decreases which makes thin accretion disks around rotating hairy black holes in Horndeski gravity more efficient than that for the Kerr black hole in general relativity. Furthermore, using the numerical ray-tracing method, we plot thin accretion disk images around these black holes and investigate the effects of hair parameter on the central shadow area of accretion disk.

We present a statistical analysis of the ages and metallicities of triple stellar systems that are known to host exoplanets. With controversial cases disregarded, so far 27 of those systems have been identified. Our analysis, based on an exploratory approach, shows that those systems are on average notably younger than stars situated in the solar neighborhood. Though the statistical significance of this result is not fully established, the most plausible explanation is a possible double selection effect due to the relatively high mass of planet-hosting stars of those systems (which spend less time on the main-sequence than low-mass stars) and that planets in triple stellar systems may be long-term orbitally unstable. The stellar metallicities are on average solar-like; however, owing to the limited number of data, this result is not inconsistent with the previous finding that stars with planets tend to be metal-rich as the deduced metallicity distribution is relatively broad.

Low-magnitude (FD(%) (geq -3%)) Forbush decreases (FDs) and their space weather linkages are recently becoming popular in the literature. Accurate timing and correct magnitude measurement of weak FDs are a desideratum. This demands disentangling the effects of the ever present cosmic ray (CR) diurnal wave that exerts undesirable influence on CR data. An enhanced version of a recently developed algorithm has been deployed to decompose raw CR data at Apatity (APTY) and Moscow (MOSC) neutron monitor (NM) stations into low and high frequency signals. A subroutine in the Fast Fourier transform software simultaneously calculates the magnitude and the epoch time of the events from the transformed data. The software selected 335 and 359 low magnitude FDs respectively for APTY and MOSC observatories. The large catalogues of low-amplitude FDs selected compared to those in literature may be attributed to the efficiency of the present algorithm. We carried out a regression analysis on the magnitude of these events and the corresponding solar wind disturbance agents. The analysis shows that for the APTY NM station, the correlation coefficient results (r) for FD-interplanetary magnetic field (IMF) and FD-planetary geomagnetic activity index (ap) relations are statistically significant at 95% confidence level. At the MOSC station, we find (r) ∼ −0.41 statistically significant at 95% confidence level for FD-solar wind speed (SWS) relation (after removing events due to co-rotating interaction regions). Analyzing all (low- and high-amplitude) FDs, (r) is relatively strong and statistically significant at 95% confidence level. The implications of these findings are discussed.

This observational study investigates the effects of interaction on the kinematics and chemical abundance of the peculiar galaxy ESO 287-IG50, which may be a polar ring galaxy in an ongoing formation process. The study utilized BVRI broad band imagery and longslit spectroscopy in the wavelength range of 4240-8700 Å. The STARLIGHT stellar population synthesis code was used to analyze the data, and standard diagnostic diagrams were employed to classify the main ionizing source of selected emission-line regions. Image analysis using filtering techniques revealed an inner ring with perpendicular structures at both ends, which could be the inner part of a bisymmetric spiral structure. Photometric analysis showed dusty filaments crossing the central structure, which was identified as the redder region of the galaxy, dominated by a non-negligible amount of dust. Shell-like structures, which could be remnants of a galaxy merging process, were also found. Image analysis through filtering revealed what appears to be an inner ring, with perpendicular structures at both ends, which could be the inner part of a bisymmetric spiral structure. Photometric analysis shows dusty filaments crossing the central structure. This region would be dominated by a non negligible amount of dust, identified as the redder region of the galaxy. A heliocentric radial velocity of 17 689±45 km s⁻¹ was measured, and the velocity profile exhibited a clear rotational behavior, with peak velocities of 110 km s⁻¹ to the SW and 80 km s⁻¹ to the other side. The analysis of the nuclear region using the STARLIGHT code revealed a stellar population consisting of approximately one-third young stars and two-thirds old stars. The predominance of an aged stellar population, a distinctive feature in galaxies undergoing interaction processes, can be attributed to the prolonged evolutionary period of this galaxy, as evidenced by the shell structures we identified as indicators of this interaction process. The [NII](lambda )6584Å/H(alpha ) ratio suggests that ESO 287-IG50 may be an AGN due to the excess of Nitrogen relative to Hydrogen in the residual spectrum, a feature not yet reported in the literature. Studying the line ratios and EW(H(alpha )), we notice that this galaxy exhibits a peculiar AGN, with a non-stellar origin ionization mechanism.