pp 279-290 September 2012
Relativistic Beaming and Orientation Effects in BL Lacertae Objects
F. C. Odo A. A. Ubachukwu A. E. Chukwude
We use the correlation between the core-to-lobe radio luminosity ratio (𝑅) and the linear size (𝐷) of a sample of BL Lacertae objects to investigate the relativistic beaming and radio source orientation paradigm for high peaked and low-peaked BL Lacs (X-ray and radio selected BL Lacs respectively) and to constrain relativistic beaming model for this extreme class of active galactic nuclei. We show that the 𝑅 - 𝐷 distributions of the BL Lac populations contradict blazar orientation sequence, with the X-ray selected BL Lacs (XBLs) being more consistent with the beaming and orientation model. On the premise that Fanaroff-Riley Type I radio galaxies are the unbeamed parent population of these objects, we derive the bulk Lorentz factor of the jets, 𝛾 ∼ 7-20 corresponding to a critical cone angle for optimum boosting, 𝜙_{c} of ∼ 1° - 4°, while on average, these objects are inclined at 5° - 12° to the line-of-sight. The implications of these results for the blazar unification sequence are discussed.
pp 291-301 September 2012
Photoionization Cross-Section of Chlorine-like Iron
Sunny Aggarwal Jagjit Singh A. K. S. Jha Man Mohan
Semi-relativistic calculations are performed for the photoionization of Fe X (an important coronal ion) from its ground state 3s^{2}3p^{5}($^{2}P^{0}_{3/2}$) and the first two excited states 3s^{2}3p^{5}(${}^{2}P^{0}_{1/2}$) and 3s3p^{6}(${}^{2}S_{1/2}$) using the Breit–Pauli 𝑅-matrix method. A lowest 41 state eigenfunction expansion for Fe XI is employed to ensure an extensive treatment of auto ionizing resonances that affect the effective cross-sections. In the present calculations, we have considered all the important physical effects like channel coupling, exchange and short range correlation. The present calculations using the lowest 41 target levels of Fe XI in the LSJ coupling scheme are reported and we expect that the present results should enable more accurate modelling of the emission spectrum of highly excited plasma from the optical to the far UV region.
pp 303-310 September 2012
Constraints on the Moment of Inertia of a Proto Neutron Star from the Hyperon Coupling Constants
The influence of the hyperon coupling constants on the moment of inertia of a proto neutron star has been investigated within the framework of relativistic mean field theory for the baryon octet {𝑛, 𝑝, 𝛬, 𝛴^{-}, 𝛴^{0}, 𝛴^{+}, Ξ^{-}, Ξ^{0}} system. It is found that for a proto neutron star, the mass, the moment of inertia and their own maximum values as a function of radius 𝑅 or 𝑀/𝑅 are all more sensitive to the hyperon coupling constants. For all the different hyperon coupling constants mentioned, the case of no hyperons corresponds to the largest moment of inertia.
pp 311-347 September 2012
Within the context of general relativity theory we calculate, analytically, scattering signatures around a gravitational singularity: angular and time distributions of scattered massive objects and photons and the time and space modulation of Doppler effects. Additionally, the scattering and absorption cross sections for the gravitational interactions are calculated. The results of numerical simulations of the trajectories are compared with the analytical results.
pp 349-359 September 2012
In the following paper, certain black hole dynamic potentials have been developed definitively on the lines of classical thermodynamics. These potentials have been refined in view of the small differences in the equations of the laws of black hole dynamics as given by Bekenstein and those of thermodynamics. Nine fundamental black hole dynamical relations have been developed akin to the four fundamental thermodynamic relations of Maxwell. The specific heats 𝐶_{𝛺,𝛷} and 𝐶_{𝐽,𝑄} have been defined. For a black hole, these quantities are negative. The 𝜅d𝐴 equation has been obtained as an application of these fundamental relations. Time reversible processes observing constancy of surface gravity are considered and an equation connecting the internal energy of the black hole 𝐸, the additional available energy defined as the first free energy function 𝐾, and the surface gravity 𝜅, has been obtained. Finally as a further application of the fundamental relations, it has been proved for a homogeneous gravitational field in black hole space times or a de Sitter black hole that $C_{\Omega,\Phi}-C_{J,Q}=\kappa \left[\left(\dfrac{\partial J}{\partial \kappa}\right)_{\Omega,\Phi}\left(\dfrac{\partial \Omega}{\partial \kappa}\right)_{J,Q}+\left(\dfrac{\partial Q}{\partial \kappa}\right)_{\Omega,\Phi}\left(\dfrac{\partial\Phi}{\partial \kappa}\right)_{J,Q}\right]$. This is dubbed as the homogeneous fluid approximation in context of the black holes.
Volume 41, 2020
All articles
Continuous Article Publishing mode
Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.
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