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tokens: of higher frequency as well as others due to nonlinear interactions of the flows. Our present simulations indeed show complex timing properties of the radiation as well as the flow dynamics. For this, we chose the flow to have an accretion rate () below the Eddington limit for all of the cases we studied. The exponent α in the cooling rate was varied from 0.5 (bremsstrahlung) to 0.6 to observe the effects of the strength of cooling on the oscillation of shocks. The specific angular momentum λ was chosen based on the recent study by Deb et al. ( 2017 ), where an onset of vertical oscillation was seen between the two values chosen here. The variation of the radius of the neutron star had a more complex effect as it controlled the effects of radiation pressure on the hydrodynamics through the parameter when a self-consistent variation is chosen. Note also that for the timescales of simulations C1 to C5, the mass and momentum deposited on the star were negligible as compared to the star’s mass and spin. This accumulation of mass and momentum would become significant for timescales of the order of years or more, which is outside the purview of the current paper. However, the energy release at the surface was found to be significant, resulting in a measurable change of T NS . We show, among other things, that the simulations produce both low- and high-frequency QPOs, and the oscillations last during the whole simulation period (more than 200 dynamical timescales measured at the injected flow radius, i.e., 30 r S ). This suggests that the QPOs are formed from a part of the flow dynamics and are not a transient effect, as inferred by others (e.g., Barret et al. 2005b ). We measure the QPO frequencies and find that both the centroid frequencies and Q factors match well with the observed results of neutron stars such as GX17+2, 4U 1728-34, and Cir X-1. We believe that the advective flow suggested in the literature, while explaining the behavior of the source Cir X-1 (Boutloukos et al. 2006 ), may be the same as the dynamic transonic flow solution we discuss here. We showed that the presence of angular momentum itself can generate multiple modes of oscillation in CENBOL and NBOL, manifesting as QPOs in the PDS, in the presence of cooling. In Figures 1 (b), 2 (c)–(d), and 3 (a), we see different types of shocks are being formed. The outer shock was found to be vertical near the equatorial plane and oblique away from the plane, very similar to what was seen for simulations around black holes ( MLC94 ). The bending instabilities reported in M01a are also found here and correspond to the hectohertz oscillations found in the PDS. So far, in the literature, a model that appears to be capable of phenomenologically addressing both timing and spectral properties is the TL model of TLM98 , who assumed the disk to be Keplerian to begin with. The viscosity was also assumed to be high enough to maintain a Keplerian distribution. The QPOs are then explained as the