Journal of Astrophysics and Astronomy最新文献

Type II solar radio bursts are commonly associated with shocks generated by coronal mass ejections (CMEs), where plasma waves are excited by magnetohydrodynamic (MHD) processes and converted into radio waves at the local plasma frequency or its harmonics. However, there are instances where type II bursts occur in the absence of whitelight CMEs. We analysed one such metric type II radio burst observed on 2 November 2023, characterized by split band features and fundamental-harmonic lanes. Notably, no CME was detected with space-based coronagraphs during this event. However, an intense M1.6 class flare was observed just before the type II burst and an extreme ultraviolet (EUV) disturbance was observed expanding into surrounding regions. The absence of any whitelight CME seen in any coronagraph field of view, even though the EUV shock had a moderate speed of ({approx }500) km s(^{-1}), which was close to the shock speed derived from radio observations. These observations indicate that the shock in the inner corona was most likely driven by the EUV ejecta seen in the lower corona, but the ejecta did not survive as a CME in the coronagraph field of view.

The paper is an investigation of the motion of a spacecraft around triangular libration points of the restricted five-body problem (R5BP) and its stability. With the assumption that the spacecraft moves in gravitational environments of four primaries, the configuration is such that the first primary is located at the origin of the coordinate system, while the second primary is collinear with the first primary, and the third and fourth are located above and below, on the left of the first primary. The equations of motion are established, and the locations of the libration points, zero velocity curve, stability of the libration points, and the Poincaré surfaces of sections are thoroughly investigated analytically and numerically when the mass of the first primary is varied. It is observed that when the mass of the first primary is increasing, the position of the spacecraft drifts away from the first primary. Further, it is seen that the increasing mass of the first primary reduces the region where motion of the spacecraft is allowed around the triangular points. Finally, the Poincaré Surface of section was explored, and it was seen that as the mass of the first primary is increasing, more clusters were noticed around the primaries, and this shows the presence of stable or quasi-periodic orbits, which correspond to regular motion. Consequently, the orbits are stable. The problem can be applied to study the motion of a spacecraft in the environments of Jupiter and its three Moons.

In this paper, we report the detailed spectral and temporal properties of six non-nuclear X-ray point sources, namely X-1, X-2, X-3, X-4, X-5, and X-6, located in the Seyfert 2 galaxy, NGC 4602, utilising the archival XMM-Newton data. Spectral fitting was performed using two empirical models: an absorbed power-law model and an absorbed disk blackbody model. Based on the estimated bolometric luminosity, all six sources fall in the ultraluminous X-ray sources range, with three out of the six sources (X-1, X-3, and X-6) reaching the extreme-luminosity X-ray luminosity range, exceeding (10^{40}) erg s(^{-1}), even in their lower limits. Detailed spectral analysis reveals distinct states among the sources. The sources, X-1, X-2, and X-4 exhibit hard spectral state with the powerlaw photon indices (Gamma ) ranging from (sim )1.69 to (sim )1.79 and inner disk temperatures (kT_{in}sim 0.65)–1.54 keV, within the error limits, while the sources, X-3, X-5, and X-6 display soft spectra with (Gamma sim 1.97)–2.43 with the cooler disk temperatures lying between (kT_{in} sim 0.28) and 0.44 keV. In this work, the Luminosity–Temperature relation could not be tightly constrained due to limited data availability, but the validity of (textrm{L} sim text {T}^{4}) relation was taken into account for the purpose of mass estimation. The hard spectral state of the sources (X-1, X-2, and X-4) may be attributed either due to the inverse comptonization of soft seed photons from the hot corona or due to the emission from the innermost region of the accretion flow while the soft spectra of the sources (X-3, X-5, and X-6) could be interpreted either as a thermal emission associated with an outflowing wind or emission from the accretion disk itself. The sources exhibit no short-term temporal variability as indicated by the Chi-square probability of constancy values, which is further complemented by the ( 3sigma ) upper limit values of RMS fractional variability. Moreover, the power density spectra created show no sign of pulsations in these sources.

In this work, we examine the dynamic motion of a test particle possessing both electrical charge and magnetic dipole moment in the presence of a Reissner–Nordström (RN) black hole (BH) situated within an externally asymptotically uniform magnetic field. The interaction between the external magnetic field and the motion of the test particle near the black hole was primarily discussed through the Lorentz force. In our study, the peak value of the effective potential of the particles decreases with increasing magnetic coupling parameter, (beta ). Additionally, the effects of the magnetic coupling parameter and the cyclotron frequency (omega _0) on the specific energy and angular momentum of the test particles for stable circular orbits are analyzed. An increase in both (beta ) and (omega _0) is found to cause a decrease in both the specific energy and angular momentum of the test particles. We also derive the expression of magnetic coupling parameters for the black hole, and the correspondence to the external magnetic field is analyzed. Our study also focuses on the center-of-mass energy, (E_{cm}), of colliding particles. An increase in the magnetic coupling parameter leads to a decrease in the center-of-mass energy extracted by the collision of two particles.

Photometric classification of Type Ia supernovae (SNe Ia) is critical for cosmological studies but remains difficult due to class imbalance and observational noise. While deep learning models have been explored, they are often resource-intensive and lack interpretability. We present a computationally efficient and interpretable classification framework that maintains high performance on imbalanced datasets. We emphasize the use of PR-AUC and F1-score as more informative metrics than ROC-AUC in severely imbalanced settings. Using an XGBoost ensemble optimized via Bayesian hyperparameter tuning, we classified light curves from the Supernova Photometric Classification Challenge (SPCC), comprising 21,318 events with a 3.19 imbalance ratio (non-Ia to Ia). Our model achieved a PR-AUC of (0.993^{+0.03}_{-0.02}), an F1-score of (0.923 pm 0.008), and a ROC-AUC of (0.976 pm 0.004), matching or exceeding deep learning performance on precision-recall trade-offs, while using fewer resources. Despite slightly lower overall accuracy, our method balances false positives and false negatives, improving the efficiency of spectroscopic follow-up. We show that optimized ensemble models offer a reproducible and lightweight alternative to complex architectures, particularly for large-scale surveys, such as the Legacy Survey of Space and Time (LSST), where transparency and efficiency are essential.

Coronal mass ejections (CMEs) are one of the primary sources of space weather disturbances and associated geomagnetic storms on Earth. Magnetohydrodynamic simulations of magnetic flux ropes are being actively investigated as a method for forecasting CME arrival times, the distributions of the solar wind plasma, and the magnetic field. To succeed, it is important to constrain the properties of such flux ropes using observations. Local simulations of the solar corona make it possible to model CME eruptions, provided that the observational data are sufficient to specify adequate boundary conditions at the solar surface. However, these simulations are limited to local, wedge-shaped domains of the solar corona because global modeling of such eruptions can be too computationally expensive. In this work, we demonstrate that it is possible to perform global simulations of flux ropes by extracting their properties obtained in the local domain and inserting them into a global model. We do that using local solutions in a wedge-shaped domain between (R_odot le rle 6 R_odot ), which are inserted into a fully-spherical global corona background between (1.03 le rle 30) (R_odot ). We also provide a detailed discussion of our simulation results, both in the local and global domains.

In this study, we investigated the spectral properties of the X-ray point sources in the giant elliptical galaxy NGC 4472 (M49), located at a distance of (sim )16.7 Mpc in the equatorial constellation of Virgo. Utilizing all available Chandra data observed using the ACIS-S detector from the year 2000 to the year 2021, we identified a total of 57 X-ray point sources, each with data counts (gtrsim )100. From the spectral study, we found 8 ultraluminous X-ray sources (ULXs) and 49 X-ray binaries (XRBs). Among the ULXs, source X-1 was found to be an extremely luminous X-ray source (ELXs) with bolometric luminosity, (L_x sim 10^{40}) erg s(^{-1}), probably accreting at a super-Eddington rate. We also detected a super-soft source, X-3, accreting at (sim )0.05 times the Eddington limit, with a disk temperature of (KT_{in} sim 0.25^{+0.06}_{-0.05}) keV. Assuming a disk blackbody model, the estimated black hole mass is ({sim } 5.57^{+8.89}_{-3.10} times 10^2 M_{odot }), placing it as a possible intermediate-mass black hole (IMBH) candidate. Source X-4 showed notable variability in luminosity, which closely correlated with changes in its inner disk temperature. Its luminosity increased as the disk temperature rose, and decreased as the temperature dropped. A similar trend was also observed in source X-14, although with comparatively less variation in luminosity. Most of the other ULXs in this study remained in a hard spectral state with consistent luminosity across observations, with the exception of source X-34, which displayed spectral variability, and source X-50, which was observed in a soft thermal state. Further, the majority of the detected X-ray binaries were found in a hard spectral state. While four of the XRBs exhibited a soft state and another four showed spectral transitions, their luminosities remained relatively stable. A color–color analysis of the X-ray sources revealed that both XRBs and ULXs generally reside within the low-mass X-ray binary (LMXB) region, albeit with enhanced spectral hardness. Notably, source X-1 displayed even greater hardness, potentially due to its higher luminosity.

Hard X-ray photons with energies in the range of hundreds of keV typically undergo Compton scattering when they are incident on a detector. In this process, an incident photon deposits a fraction of its energy at the point of incidence and continues onwards with a change in direction that depends on the amount of energy deposited. By using a pair of detectors to detect the point of incidence and the direction of the scattered photon, we can calculate the scattering direction and angle. The position of a source in the sky can be reconstructed using many Compton photon pairs from a source. We demonstrate this principle in the laboratory by using a pair of Cadmium Zinc Telluride (CZT) detectors sensitive in the energy range of 20–200 keV, similar to those used in AstroSat/CZT Imager (CZTI). The laboratory setup consists of two detectors placed perpendicular to each other in a lead-lined box. The detectors are read out by a custom-programmed Xilinx PYNQ-Z2 FPGA board, and data are then transferred to a personal computer (PC). There are two key updates from CZTI: the detectors are read concurrently rather than serially, and the time resolution has been improved from 20 to 7.5 (mu )s. We irradiated the detectors with a collimated (^{133} texttt {Ba}) source and identified Compton scattering events for the 356 keV line. We run a Compton reconstruction algorithm to correctly infer the location of the source in the detector frame, with a location-dependent angular response measure of 16(^circ )–30(^circ ). This comprises a successful technology demonstration for a Compton imaging camera in the hard X-ray regime. We present the details of our setup, the data acquisition process, and software algorithms, and showcase our results. We also quantify the limitations of this setup and discuss ways of improving the performance in future experiments.

In this study, we present our scientific approach to observationally infer possible correlations of the disruption age with the stellar surface density and two-dimensional radius for 200 open star clusters within the solar neighbourhood. A detailed statistical analysis of number density, core and tidal radius, mass, and log(age) has also been presented using the Gaia EDR3 database. The initial mass and disruption time of the individual clusters are calculated using the analytical relations available in the literature, considering the cluster mass loss mechanism due to stellar evolution and tidal interactions. Considering the mass loss models used in this study, we also observe the variation of the initial mass of the star clusters as a function of their present age. We carry out a linear fit for the variation of the cluster disruption time with its number density, which gives an approximate correlation of the form, (t_{textrm{dis}}propto rho _{o}^{0.230pm 0.052}). We also assess this linear relation using statistical correlations, which results in a moderate coefficient value of 0.3903. This statistical correlation and the power law relation illustrate that disruption time increases with the increasing stellar surface density of the cluster. We also observationally and statistically investigate the correlation between the radius and disruption time of the clusters, but no prominent dependence was found between them.

The thermodynamics of interplanetary coronal mass ejections (ICMEs) is often described using a polytropic process. Estimating the polytopic index ((gamma )) allows us to quantify the expansion or compression of the ICME plasma arising from changes in the plasma temperature. In this study, we estimate (gamma ) for protons inside the magnetic clouds (MCs), their associated sheaths, and ambient solar wind for a large sample of well-observed events observed by the Wind spacecraft at 1 AU. We find that (gamma ) shows a high (({approx }1.6)) – low (({approx } 1.05)) – high (({approx }1.2)) behavior inside the ambient solar wind, sheath, and MCs, respectively. We also find that the proton polytropic index is independent of small-scale density fluctuations. Furthermore, our results show that the stored energy inside MC plasma is not expended in expanding its cross-section at 1 AU. The sub-adiabatic nature of MC plasma implies external heating – possibly due to thermal conduction from the corona. We find that the heating gradient per unit mass from the corona to the protons of MC at 1 AU is ({approx } 0.21) erg cm(^{-1}) g(^{-1}), which is in agreement with the required proton heating budget.