2025RAA....25b5013H

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)stability properties, taking into account various values of specific angular momentum, λ₀. Within the range 10-50R_g (where R_g denotes the Schwarzschild radius), shocks are discernible for λ₀ ≥ 1.75. In the special relativistic hydrodynamic simulation when λ₀ = 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 ≤ λ₀ ≤ 1.80. Using free-free emission as a proxy for analysis, we show that the luminosity oscillations between frequencies of 0.1-10 Hz for λ₀ range as 1.7 ≤λ₀ ≤ 1.80. These findings offer insights into quasi-periodic oscillation 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 X-ray telescopes such as Chandra, Swift, and XMM-Newton.