Iranian Journal of Astronomy and Astrophysic
Volume:11 Issue: 3, Autumn 2024

Recent years have seen a growing interest in radio detection of Cosmic Rays. We investigated the incident direction of Cosmic Rays for an array of 11 radio antennas through a series of simulations using the CoREAS toolkit. We have determined that utilizing the east-west component of the electric field yields improved angular resolution for our array compared to the north-south and vertical components. Our findings reveal a significant correlation between the error in direction estimation of cosmic rays and the angle between the earth’s magnetic field and the cosmic ray’s trajectory. Specifically, for 1017 eV proton showers, we observe that the angular resolution is poorer for showers originating from the south (0.91°±0.06°) compared to those from the east (0.48±0.07), north (0.33°±0.08°), and west (0.30°±0.10°) directions. Additionally, a slight decrease (less than 0.1°) in angular resolution is noted for 1018 eV showers. This research sheds light on the impact of Earth's magnetic field on cosmic ray detection using radio antenna arrays.

Those globular clusters that are located in the halo of galaxy experience a weak gravitational force due to their great distance from the center of their host galaxy, so they are characterized by extremely low gravitational potential. This unique characteristics make them important subjects of research in various fields. The study of clusters, analyzing the dynamics and gravitational interactions within them, offers a unique opportunity to explore the implications of modified gravity theories, such as fifth force interactions or unscreened regions. In our paper, we explore the presence and extent of an unscreened region in the outer layers of an isothermal sphere, as represented by the King model and influenced by a chameleon field. Also we consider the acceleration resulting from the chameleon field and then proceed to calculate the line-of-sight velocity dispersion under the influence of the chameleon and compare it with Newtonian predictions. Our findings reveal that the dynamical impact of the fifth force can be observed throughout the entire of the globular cluster.

In this research, an analytical expression of the Weibel electromagnetic instability growth rate is investigated for strongly coupled plasma in the presence of Coulomb collisions in the beam-plasma interaction under a low-frequency wave condition. In this regard, the distribution function governing the relativistic beam and plasma particles have been considered as semi-Maxwellian and Kappa distribution functions respectively. The effect of the temperature anisotropy parameter, the spectral index, quantum and relativistic parameters on Weibel electromagnetic instability growth rate have been investigated in collisional and non-collisional states. The obtained results show that the Coulomb collision frequency of particles plays an important role in suppressing the unstable modes in isotropic plasmas due to increase in the free energy of the plasma. Therefore, it was concluded that the Weibel instability growth rate in collision state has a more stable situation than in the non-collisional state in the strongly coupled plasma with Kappa distribution function.

In [1], we have found that the curved spacetime version of the vacuum stress between conducting plates was first done in flat spacetime by Brown and Maclay. Here, we calculate the energy-momentum tensor for the Casimir effect of parallel plates under Neumann boundary conditions to support our recent results found in [2]. We use direct calculation of energy-momentum tensor by employing the well understood point splitting method of regularization, and we show that the there is first order correction to the Casimir energy in curved spacetime proportional to GM/c2R where R and M are the radius and the mass of the source of gravity.

Two competing theories, the wave theory and reconnection theory, provide explanations for solar corona heating, supported by observations of wave phenomena and magnetic reconnection on the Sun. Plasma β, the ratio of thermal plasma pressure to magnetic pressure, varies significantly in the solar corona, influencing wave propagation Throughout much of the corona, the plasma β is considerably smaller than one, to disregard pressure gradients in the plasma. However, plasma β fluctuates throughout the entire region due to the varying magnetic field, such that near null points, the magnetic field diminishes, leading to a potential increase in plasma β. This study focuses on Alfvén pulses interacting with a 2D magnetic null point, investigating the nonlinear effects of plasma beta adjustment in different layers. The study utilizes the PLUTO code, a sophisticated shock-capturing numerical framework, to model the interactions of Alfvén pulses under varying plasma β conditions. The simulations are conducted on high-resolution Cartesian grids with zero-gradient boundary conditions to ensure accuracy. By solving the magnetohydrodynamic (MHD) equations, the analysis reveals temporal fluctuations in the system’s response, with certain instances characterized by higher amplitudes and sharper peaks, indicative of intensified interactions of the Alfvén pulse. The variations in amplitude and peak sharpness underscore the dynamic nature of the system, with certain moments displaying stronger responses than others. On the one hand, when we adjust the plasma beta closer to the null point, the changes in radial velocity and density disturbance decrease, and over time, the wave energy is released more rapidly along the field lines. Density and velocity changes depend on plasma β and proximity to the null point, emphasizing the system’s sensitivity to these parameters. Therefore, it is essential to consider atmospheric conditions for accurate energy transfer assessments.

he Lyman Alpha forest is one of the most powerful cosmological tools for studying large-scale structures of the universe. The flux autocorrelation function for Lyman alpha forest is used to study the clustering of structures. This paper, uses the Lyman alpha forest of 49 high-resolution, high signal-to-noise (S/N>20) QSO spectra observed with VLT/UVES. The studied quasars have emission redshifts in the range of ( 1.89< zem < 3.80). The flux autocorrelation function is calculated for each sample, and then, the effect of metal absorption lines in the Lyman alpha forest on the flux autocorrelation function is investigated. The results of the present study show that the effect of removing metal absorption lines is more visible in the transition to lower redshifts, where there are relatively fewer Lyman alpha absorption lines. Moreover, the change in the flux autocorrelation function at different redshifts is investigated. The results indicate that the flux autocorrelation function at higher redshifts has a larger average value than that at lower redshifts.