Journal of High Energy Astrophysics最新文献

We construct asymptotically flat, static spherically symmetric black holes with regular centre in $f(R,T)$ gravity coupled to nonlinear electrodynamics Lagrangian. We obtain generalized metric function of the Bardeen and Hayward black holes. The null, weak and strong energy conditions of these solutions are discussed. All the energy conditions hold outside the black hole's outer event horizon by appropriated choices of parameters. Quasinormal mode of massive scalar perturbation is also investigated. Quasinormal frequencies are computed via the sixth order Wentzel-Kramers-Brillouin (WKB) with Padé approximation. All the imaginary parts of the frequencies are found to be negative. Finally, we provide an analysis in the eikonal limit.

It is commonly believed that galactic cosmic rays are produced in supernova remnants (SNRs) and accelerated via a diffusive shock acceleration (DSA) mechanism in supernova blast waves driven by expanding SNRs. The latest theoretical advancement of the diffusive shock acceleration hypothesis in SNRs shows that cosmic rays may be accelerated up to the knee energy of the observed cosmic ray spectrum under the amplified magnetic field scenario. There is, however, no empirical evidence to support SNRs as sources of hadrons with energies larger than a few tens of TeV. Very recently, LHAASO observatory reported the very high-energy gamma ray emission between TeV to PeV energy range from two SNRs, Cassiopeia A and IC 443. Above 25 TeV energies, non-detection of gamma-ray flux by LHAASO yields a strong upper limit. In this work, we investigate the implications of the acceleration of cosmic ray protons in the SNR on energetic gamma rays produced in the hadronic interaction of cosmic rays with ambient matter. Our findings imply that when we consider the highest attainable energy of cosmic ray protons in the SNRs to be about 100 TeV, the observed gamma-ray spectra from the two SNRs can be described consistently. Therefore, we conclude that the Cassiopia A and IC 443 SNRs are unlikely to be cosmic ray PeVatrons.

MAXI J153–571 accretion flow consists of Keplerian (optically thick) and sub-Keplerian (optically thin) flow, and their mass accretion rates seem to regulate other accretion flow characteristics. Hard X-rays are produced when the Keplerian seed soft photons are thermally or inverse comptonized in the Compton cloud/post-shock region by hot electrons. The variations/fluctuations of components of the accretion flow during the hard states create propagating Quasi-periodic oscillation (QPO) when their timescales are roughly matched and resonance phenomena occur. The QPO and its frequency are timing properties and the accretion flow spectra-temporal characteristics can be determined via spectral analysis. In this study, we looked into the accretion flow characteristics of MAXI J153–571 during the hard-intermediate state. Spectral analysis of MAXI J153–571 observed by MAXI/GSC, Swift/BAT, and NuSTAR on the same or close-in epochs was carried out. XSPEC and TCAF models were used in fitting/modeling the data. A robust and statistically acceptable fit spectra with a reduced Chi-squared value of ∼ 0.84 – 1.20 and best-fit photon index of 2.0–2.29 was obtained. The track of the accretion flow characteristics was obtained using models’–fitted parameters and MATLAB written codes of physical equations. Some accretion flow characteristics are positively correlated while others are anti-correlated at different phases and their correlation are statistically significant. The correlation of accretion flow characteristics with one another suggests that saturation effects, variation/fluctuations in the accretion flow, and intermittent/flickering behavior of MAXI J153–571 are tied to the variations/fluctuations of the intrinsic properties; mass accretion rates. Moreover, a resonance condition of 0.70 to 0.83 indicates that the cooling and infall timescales are roughly matched and affirms the presence of QPO in the accretion flow. This suggests that the origin of the photon index–QPO frequency (Γ–vQPO) relation is strongly linked to the variation/fluctuations in mass accretion flow rates. Hence, the accretion flow is dynamic, and independent variations/fluctuations of mass accretion rates could regulate the variation/fluctuations of other accretion flow parameters and perhaps, spectral evolution.

The primary aim of this study is to investigate the characteristics of particle dynamics in black holes with non-linear electrodynamics. To achieve this objective, we consider three non-linear electrodynamics black hole geometries with magnetic charge. We perform calculations and analysis to determine the horizon radius, inner stable circular orbit, and quasi-periodic oscillations, thereby uncovering the dynamical features of these systems. In-depth discussions are provided regarding the influence of magnetic charge and the non-linear electrodynamic parameter on the obtained results.

The black hole X-ray binary MAXI J1820+070 has been frequently observed by NICER since its outburst in 2018. We report the NICER observations of this black hole (BH) X-ray binary, especially during the soft state, and determine the spin of the BH with the continuum-fitting method. We finally constrain the mean spin of MAXI J1820+070 to be $a_{⁎}$=$0.38\pm 0.12$ only using NICER data in the band of 1 – 10 keV. The measured spin value is basically stable within the narrow range of 0.3 - 0.4 when the accretion disk extends into the innermost stable circular orbit (ISCO). We also check the fitted spin values combined with NICER and Insight-HXMT data from 1 – 25 keV, and find $a_{⁎}$=$0.2\pm 0.1$ which is systematically lower than that based on only NICER observations. We discuss some implications about the evolution of the disk and corona during the soft state through changes of the measured spin and mass accretion rate.

We use updated gas mass fraction measurements of 44 massive dynamically relaxed galaxy clusters collated in Mantz et al. (2022) to distinguish between the standard ΛCDM model and $R_h=ct$ universe. For this purpose, we use Bayesian model selection to compare the efficacy of both these cosmological models given the data. The gas mass fraction is modeled using both cosmology-dependent terms and also astrophysical parameters, which account for the variation with cluster mass and redshift. We used two different prior choices for some of the astrophysical parameters. We find a Bayes factors of 50 and 5 for ΛCDM as compared to $R_h=ct$ for these two prior choices. This implies that ΛCDM is favored compared to $R_h=ct$ with significance ranging from substantial to very strong.

The Hawking evaporation process has important implications for our understanding of the universe, as it suggests that black holes are not eternal and can eventually evaporate away completely. We evaluate the Hawking evaporation process of AdS Schwarzschild scalar-tensor-vector gravity black hole by using Stefan-Boltzmann law and find out that Hawking evaporation rate depends on the AdS radius l and deviation parameter α of the scalar-tensor-vector gravity. We analyze that for small values of AdS radius l and positive deviation parameter α black hole evaporates quickly. While there is exponential increase in lifetime of the black hole for large AdS radius l and negative deviation parameter α. Moreover, we find out thermodynamical quantities like Helmholtz free energy, internal energy, pressure, enthalpy, Gibbs free energy and specific heat and show that how deviation parameter α and the correction parameter ζ of the first order corrected entropy play vital role on the stability and phase transitions of the black holes.

The problem of Astrophysical Jet formation from relativistic accretion disks through the establishment of relativistic disk-powerful jet equilibrium structure is studied applying the Beltrami-Bernoulli equilibrium approach of Shatashvili and Yoshida 2011; Arshilava et al. 2019. Accretion disk is weakly magnetized consisting of fully ionized relativistic electron-ion plasma and photon gas strongly coupled to electrons due to Thompson Scattering. Analysis is based on the generalized Shakura-Sunyaev α-turbulent dissipation model for local viscosity (being the main source of accretion), in which the contributions from both the photon and ion gases are taken into account. Ignoring the self-gravitation in the disk we constructed the analytical self-similar solutions for the equilibrium relativistic disk-jet structure characteristic parameters in the field of gravitating central compact object for the force-free condition. It is shown, that the magnetic field energy in the Jet is several orders greater compared to that of accretion disk, while jet-outflow is locally Super-Alfvénic with local Plasma-beta <1 near the jet-axis. The derived solutions can be used to analyze the astrophysical jets observed in binary systems during the star formation process linking the jet properties with the parameters of relativistic accretion disks of electron-ion-photon gas.

Cosmic repulsion represented by a small positive value of the cosmological constant changes significantly properties of central gravitational fields at large distances, leading to existence of a static (or turnaround) radius where gravitational attraction of a center is just balanced by cosmic repulsion. Analyzing behavior of radial timelike geodesics in the Schwarzschild–de Sitter spacetime near its static radius we show that the particles with specific energy close to unity have tendency to slow down and cluster just below the static radius, forming clumps which, subsequently, start to expand uniformly due to cosmic repulsion. For central masses of $({10}^6$–${10}^{11})M_{\odot }$ and current value of the cosmological constant $1.1\times {10}^{-52}$ ${\text{m}}^{-2}$, this phenomenon takes place at distances of tens to hundreds of kiloparsecs from the center, being comparable with distances in which huge radio-lobes from some active galaxies were observed.