Relativistic Accretion Flow in a Generic Class of Spherically Symmetric Static Spacetime
We investigate the properties of low angular momentum, inviscid, advective accretion flows in a generic static and spherically symmetric spacetime that incorporates higher-order corrections up to the fourth order in $1/r$. Employing this metric, we self-consistently solve the relativistic hydrodynamical equations and obtain the family of global transonic accretion solutions ($O$, $A$, $W$ and $I$-types) by means of the spacetime parameters ($\delta$, $\eta$, $\beta$) and the flow parameters (specific energy $\mathscr{E}$ and angular momentum $\lambda$). Our analysis reveals that the accretion flow possesses either single or multiple critical points depending on these input parameters. We delineate the regions of the $\delta-\lambda$ and $\lambda-\mathscr{E}$ parameter spaces that admits solutions with multiple critical points and demonstrate how these regions evolve with increasing spacetime parameter $\delta$. Furthermore, while connecting the spacetime geometry with observable signatures, we compute the spectral energy distribution (SED) from thermal bremsstrahlung emission and observe that increasing $\delta$ enhances the SED relative to the Schwarzschild case. Finally, we find that global transonic solutions harbouring inner critical points ($I$-types) yields more luminous power than those with only outer critical points ($O$ and $A$ types).