Discovery of an Accretion-rate Independent Absolute RMS Amplitude of Millihertz Quasi-periodic Oscillations in 4U 1636-53
Ming Lyu ... [et al.].
Serie: Trabajos publicados del IAR ; no. 1526
Resumen: We investigate the frequency and amplitude of the millihertz quasi-periodic oscillations (mHz QPOs) in the neutron-star low-mass X-raybinary 4U 1636-53 using Rossi X-ray Timing Explorer observations. Wefind that no mHz QPOs appear when the source is in the hard spectralstate. We also find that there is no significant correlation between thefrequency and the fractional RMS amplitude of the mHz QPOs.Notwithstanding, for the first time, we find that the absolute rmsamplitude of the mHz QPOs is insensitive to the parameter S a, which measures the position of the source in the color-colordiagram and is usually assumed to be an increasing function of massaccretion rate. This finding indicates that the transition frommarginally stable burning to stable burning or unstable burning couldhappen very rapidly since, before the transition, the mHz QPOs do notgradually decay as the rate further changes