Study of relativistic accretion flow around KTN black hole with shocks

Abstract

We present the global solutions of low angular momentum, inviscid, advective accretion flow around Kerr-Taub-NUT (KTN) black hole in presence and absence of shock waves. These solutions are obtained by solving the governing equations that describe the relativistic accretion flow in KTN spacetime which is characterized by the Kerr parameter ($a_{\rm k}$) and NUT parameter ($n$). During accretion, rotating flow experiences centrifugal barrier that eventually triggers the discontinuous shock transition provided the relativistic shock conditions are satisfied. In reality, the viability of shocked accretion solution appears more generic over the shock free solution as the former possesses high entropy content at the inner edge of the disc. Due to shock compression, the post-shock flow (equivalently post-shock corona, hereafter PSC) becomes hot and dense, and therefore, can produce high energy radiations after reprocessing the soft photons from the pre-shock flow via inverse Comptonization. In general, PSC is characterized by the shock properties, namely shock location ($r_s$), compression ratio ($R$) and shock strength ($S$), and we examine their dependencies on the energy (${\cal E}$) and angular momentum ($\lambda$) of the flow as well as black hole parameters. We identify the effective domain of the parameter space in $\lambda-{\cal E}$ plane for shock and observe that shock continues to form for wide range of flow parameters. We also find that $a_{\rm k}$ and $n$ act oppositely in determining the shock properties and shock parameter space. Finally, we calculate the disc luminosity ($L$) considering free-free emissions and observe that accretion flows containing shocks are more luminous compared to the shock free solutions.Comment: 14 pages, 12 figures, Submitted for publication in PR