Study of magnetized accretion flow with variable $\Gamma$ equation of state

TL;DR

This paper investigates magnetized accretion flows onto neutron stars with a variable gamma equation of state, including cooling processes, revealing shock formations and flow behaviors influenced by star rotation and composition.

Contribution

It introduces a comprehensive model of magnetized accretion with a temperature-dependent equation of state and cooling effects, analyzing shock formation and flow structures near neutron stars.

Findings

All accretion solutions terminate with a shock near the star surface.

Multiple sonic points and secondary shocks can form for certain star rotation periods.

Cooling processes like bremsstrahlung and cyclotron are essential for realistic solutions.

Abstract

We present here the solutions of magnetized accretion flows on to a compact object with hard surface such as neutron stars. The magnetic field of the central star is assumed dipolar and the magnetic axis is assumed to be aligned with the rotation axis of the star. We have used an equation of state for the accreting fluid in which the adiabatic index is dependent on temperature and composition of the flow. We have also included cooling processes like bremsstrahlung and cyclotron processes in the accretion flow. We found all possible accretion solutions. All accretion solutions terminate with a shock very near to the star surface and the height of this primary shock do not vary much with either the spin period or the Bernoulli parameter of the flow, although the strength of the shock may vary with the period. For moderately rotating central star there are possible formation of multiple sonic points in the flow and therefore, a second shock far away from the star surface may also form. However, the second shock is much weaker than the primary one near the surface. We found that if rotation period is below a certain value $(\pmin)$, then multiple critical points or multiple shocks are not possible and $\pmin$ depends upon the composition of the flow. We also found that cooling effect dominates after the shock and that the cyclotron and the bremsstrahlung cooling processes should be considered to obtain a consistent accretion solution.