The harmonic component of the millihertz quasi-periodic oscillations in 4U 1636-53

Abstract

We studied the harmonics of the millihertz quasi-periodic oscillations (mHz QPOs) in the neutron-star low-mass X-ray binary 4U 1636-53 using the Rossi X-ray Timing Explorer observations. We detected the harmonics of the mHz QPOs in 73 data intervals, with most of them in the transitional spectra state. We found that the ratio between the rms amplitude of the harmonic and that of the fundamental remains constant in a wide range of the fundamental frequency. More importantly, we studied, for the first time, the rms amplitude of the harmonics vs. energy in 4U 1636-53 in the 2-5 keV range. We found that the rms amplitude of both the harmonic and the fundamental shows a decreasing trend as the energy increases, which is different from the behaviors reported in QPOs in certain black hole systems. Furthermore, our results suggest that not all observations with mHz QPOs have the harmonic component, although the reason behind this is still unclear.

17 pages, 10 figures, accepted by ApJ

References in corpus (6)

• X-ray time variability across the atoll source states of 4U 1636--53
• Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-ray Bursts
• Reaction Rate and Composition Dependence of the Stability of Thermonuclear Burning on Accreting Neutron Stars
• Millihertz quasi-periodic oscillations in 4U 1636-53 associated with bursts with positive convexity only
• XMM-Newton and NICER measurement of the rms spectrum of the millihertz quasi-periodic oscillations in the neutron-star low-mass X-ray binary 4U 1636-53
• Discovery of an accretion-rate independent absolute RMS amplitude of millihertz quasi-periodic oscillations in 4U 1636-53

Cited by in corpus (2)

• Detection of millihertz quasi-periodic oscillations in the low-mass X-ray binary 4U 1730--22 with NICER
• Detection of a strong ~2.5 Hz modulation in the Newly Discovered Millisecond Pulsar MAXI J1816-195