Astrophysics and Space Science最新文献

This study focus on atypical Type II radio bursts observed in conjunction with three simultaneous coronal mass ejections (CMEs) on September 27, 2001. These CMEs originated from a single active region (AR) and were linked to relatively weak solar flares. Analysis of the CME sequences revealed distinct periods of interplanetary (IP) Type II radio emissions, characterized by pronounced increases in intensity. The first radio enhancement, lasting 20 minutes, exhibited very low density and frequency (1.65–1.5 MHz) at a height range of (7.8–8.2) solar radii (). Subsequently, the second radio signature persisted for 40 minutes with a frequency range of (900–700) kHz and a height range of (10.9–12.6) . The third radio signature spanned 1 hour and 20 minutes, featuring a frequency range of (660–390) kHz and a height range of (13.2–18.6) . The fourth enhancement extended over 3 hours, ranging from (550–250) kHz in frequency and (14.6–25.0) in height. We concluded that the initial low-density radio signature resulted from a shock wave generated by reconnection of magnetic field lines, without an intense flare or extreme ultraviolet imaging telescope (EIT) wave. This shock wave then accelerated subsequent CMEs. Alternatively, the radio burst could have formed in the wake of the initial slow CME, creating a low-density environment. The second radio enhancement coincided with the accelerated propagation of CME1’s core and was attributed to enhanced radio emission resulting from the Type II shock encountering filament material. The third radio enhancement aligned with the concept of a CME bow shock, indicating that the shock was positioned at the leading front of the CME. This enhancement occurred when the shock met remnant material from earlier CMEs, yet the shock continued propagating at a constant speed. The fourth enhancement progressed to higher frequencies due to the merging of CME1’s core with CME2, propagating along CME3’s path. This comprehensive analysis provides valuable insights into the complex dynamics and interactions associated with these unique Type II radio bursts and their correlation with coronal mass ejections.

For Galactic RRab stars 121 empirical and semiempirical metallicity–absolute magnitude relations known since 1990 are analyzed. For these variables, using their known empirical data, relations are determined between the mass, the radius, the effective surface temperature, the bolometric correction, the luminosity, the absolute magnitude, on the one hand, and the metallicity and the pulsation period, on the other hand. Using these relations, the empirical value of the Eddington pulsation constant is accurately determined for RRab stars for the first time.

X-ray binaries are known to exhibit different spectral states which are often associated with different black hole accretion modes. The exact geometry and properties of these accretion modes is still uncertain. Recent IXPE measurements of linear polarization of X-ray emission in canonical X-ray binary system Cygnus X-1 allow us to test models for the hard spectral state of accretion in a unique way. We show that general relativistic radiative magnetohydrodynamic (GRRMHD) simulations of accreting stellar black hole in a hard X-ray state may be consistent with the new observational information. In the presented framework, where first-principle models have limited number of free parameters, the polarimetric X-ray observations put constraints on the viewing angle of the inner hot accretion flow.

This work studies the motion around irregular elongated asteroids through two approaches. Firstly, it revisits the dipole-segment model, identifying families of periodic orbits for asymmetric mass distribution. Additionally, a new model incorporating variable density for elongated asteroids is introduced and compared to the dipole-segment model. Several families of periodic orbits have been found through continuation of planar orbits and out-of-plane bifurcation processes, obtaining results in agreement with previous studies about the dynamics around irregular asteroids. This highlights the relevance of simple mathematical models in studying asteroid dynamics and the importance of accounting for density and geometric properties. Although the families of periodic orbits studied in this work are not comprehensively sampled, they constitute an example of the variety of orbits that can be followed by a particle orbiting the asteroid, helping us to better understand the dynamics around these elongated bodies.

We utilized the Forbush decreases (magnitude (>1.5%)) detected in cosmic ray neutron monitor data during continuous five solar cycles, viz., 20, 21, 22, 23 and 24 (1965 to 2019) and subjected them to wavelet analysis in order to obtain the possible periodicities in their occurrence. We also studied the periodicities separately during the odd and even solar activity cycles. In addition to solar activity, the solar magnetic polarity and its extension into the interplanetary space makes significant difference in the cosmic ray modulation in the helisphere, we have also applied the wavelet analysis procedure separately during positive (A > 0) and negative (A < 0) polarity states of the heliospheric magnetic fields. Observed periodicities in Forbush decreases have been discussed and compared with earlier detected periodicities in solar and geomagnetic activity indices, e.g., sunspot numbers, sunspot areas, sunspot groups, solar flares, coronal mass ejections, and various geomagnetic activity indices. Significant short-term periodic behaviour detected in the occurrence of Forbush decreases, which in general, corroborates the observed behaviour in solar (in particular, solar eruptive activity) and geomagnetic activity. Understanding the quasi-periodic process in magnetic field emergence from solar active regions and solar eruptive activity, as well as solar-terrestrial coupling and space weather effects, requires comparing the quasi-periodic behaviour between parameters representing solar and geomagnetic activity along with cosmic ray variability.

We have proposed that galaxy formation is catalyzed by the collision of infalling and outstreaming particles from leaky, horizonless astrophysical black holes, most likely gravastars, and based on this gave a model for the disk galaxy scale length. In this paper we modify our original scale length formula by including an activation probability (P) for a collision to lead to nucleation of star formation. The revised formula extrapolates from early universe JWST data to late time data to within a factor of five, and suggests that galaxy dimensions should systematically get smaller as the observed redshift z increases. We also show that particles recycling through gravastars can lead to a reduction in the temperature of the surrounding gas, through a “heat pump” refrigeration effect. This can trigger galaxy formation through enhanced star formation in the vicinity of the gravastar.

In this work we have studied about the characteristics and dynamical changes during the recovery time of moderate and strong geomagnetic storms of ((mathrm{Dst}<-50text{ nT})). In our investigation of 57 storms triggered by CMEs/CIRs, we concentrated on the solar wind’s influence on their decay phases. Selected storms were classified into distinct groups based on their recovery characteristics. Employing the superposed epoch analysis and best fit methods, we scrutinized several interplanetary solar wind plasma and field parameters and their various functions. The analysis encompassed various single, dual, and multiple interplanetary plasma and field parameters/functions. We determined the most representative characteristic time for the storm’s recovery profile by carefully fitting an exponential curve. A correlation analysis between Dst and solar wind parameters/functions led us to isolate a coupling function ((rho ^{frac{1}{2}}mathrm{Ey})) which best described the decay rate of the ring current. It shows that electric field term (Ey) coupled with a viscus term ((rho ^{frac{1}{2}})) plays pivotal role in determining the recovery rate of a geomagnetic storms. Additionally, we modeled the complex patterns of Dst recovery in relation to solar wind parameters and functions using a second-order polynomial. Remarkably, during the recovery phase, a dynamic correlation between Dst and solar wind parameters/functions was revealed. The three-parameter solar wind-magnetosphere electrodynamical coupling functions, which combines the viscus term ((rho ^{frac{1}{2}})) and the electric field-related function ((mathrm{v}^{frac{4}{3}}mathrm{B})) ((rho ^{frac{1}{2}}mathrm{v}^{frac{4}{3}}mathrm{B})), significantly impacts the recovery phase of geomagnetic disturbances. Our investigation extended to the relationship between main and recovery phase durations, providing valuable insights into the solar wind’s intricate control over the decay of the geomagnetic disturbances. These findings contribute significantly to advancing our comprehension of the complex relationship between solar wind dynamics and the evolution of geomagnetic disturbances.

Incompressible vortex flow are observed in a large variety of astrophysical plasmas such as the convection zone and the atmosphere of stars, in astrophysical jets in stellar winds and in planetary magnetospheres. More specifically, magnetohydrodynamic (MHD) simulations have shown that two large scale interlaced Alfvénic vortices structure the magnetic tail of Uranus at solstice time. Assuming identical vortices, we compute the general linear structure of the flow near their centers within the frame of ideal MHD. We then use the analytic results to interpret and qualify the vortices observed in a 3D MHD simulation of a fast rotating Uranus-type planet.

This study investigates contributions of solar radiation and geomagnetic activity of consecutive 27-day recurrent geomagnetic storms (RGSs) to the variabilities in the equatorial ionospheric F-region in American Peruvian sector during 2007. Results show the ionospheric responses to the RGSs are quasi-periodic and multifaceted with highly evolved in the summer months. In High-Intensity Long-Duration Continuous (AE) Activity (HILDCAA) events, the ionospheric responses are more variable than in non-HILDCAA. The critical frequency and peak height of the F-layer tend to increase during storm-time in summer months. The maximum density enhancements are more than 70% in the three RGSs and they are long-lasting in the summer months. A new classification of daily variations in the virtual height of the F-layer ((h'F)) is proposed: Mode A shows mixing of great height before noon and low height near midnight, Mode B shows moderate height near midnight, and Mode C shows mixing of high height before noon and great height near midnight. These (h'F) Modes efficiently characterize the ionospheric variabilities and processes. The great uplifts of (h'F) during night-time in the summer months coincide with the presence of strong disturbance dynamo electric fields and disturbed neutral winds generated by intensified Joule heating. The solar EUV plays a role in the uplifts of (h'F) during the daytime. Zonal electric field disturbances and perturbations in the neutral meridional winds critically contribute to the equatorial ionospheric responses and ESF variabilities. Most cases of inhibited/suppressed ESF were observed in Mode A and occurred under overshielding conditions. The inhibited ESF associated with (h'F) not raised in the recovery phase is mainly contributed by a cooling state after great uplifts by daytime thermospheric winds.

Solar surges are collimated flows of plasma that occur in the periphery of active regions (ARs). The kinematics, physical properties, and triggering mechanisms of a solar surge were studied through imaging and spectroscopic diagnosis. The surge has a typical inverted Y-shape, and it moves with a speed of more than 200 km/s in the transition-region (TR) which is much higher than the sound speed of TR. The observational findings suggest that the surge was triggered due to magnetic reconnection. In addition, a hot jet formed after around 03 minutes and propagated at a speed that is comparable to the sound speed of the corona. Hence, most probably, the hot jet forms due to the chromospheric evaporation. The spectroscopic diagnosis reveals that electron densities are log₁₀ 10.82±0.90 and log₁₀ 9.93±1.27 in the base and spire of the surge, respectively. Further, it is found that the Si iv line ratio is around 1.85 in the base and 1.80 in the spire of the surge. Hence, we say that most of the Si iv profiles are forming under optically thick conditions in the surge. Most importantly, some Si iv spectral profiles from the base and spire of the surge are double peak profiles with a dip close to the central wavelength. Also, in the same region, optically thick conditions exist, therefore, most probably, the central dip in the profiles is a result of the self-absorption. This is the first-ever report of self-absorption in the solar surges.