Relativistic Low Angular Momentum Advective Flows onto Black Hole and associated observational signatures

We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their (in)stabilities properties taking into account various specific angular momentum, ${\lambda }_0$. Within the range $10-50R_g$ (where $R_g$ denotes the Schwarzschild radius), shocks are discernible for ${\lambda }_0\ge 1.75$. In the special relativistic hydrodynamic (RHD) simulation when ${\lambda }_0=1.80$, we find the merger of two shocks resulted in a dramatic increase in luminosity. We present the impact of external and internal flow collisions from the funnel region on luminosity. Notably, oscillatory behavior characterizes shocks within $1.70\le {\lambda }_0\le 1.80$. Using free-free emission as a proxy for analysis, we shows that the luminosity oscillations between frequencies of $0.1-10$ Hz for ${\lambda }_0$ range $1.7\le {\lambda }_0\le 1.80$. These findings offer insights into quasi-periodic oscillations emissions from certain black hole X-ray binaries, exemplified by GX 339-4. Furthermore, for the supermassive black hole at the Milky Way’s center, Sgr A*, oscillation frequencies between ${10}^{-6}$ and ${10}^{-5}$ Hz were observed. This frequency range, translating to one cycle every few days, aligns with observational data from the X-ray telescopes such as Chandra, Swift, and XMM-Newton.