Millihertz quasi-periodic oscillations in 4U 1636-53 associated with bursts with positive convexity only

Abstract

We investigated the convexity of all type I X-ray bursts with millihertz quasi-periodic oscillations (mHz QPOs) in 4U 1636-53 using archival observations with the Rossi X-ray Timing Explorer. We found that, at a 3.5 $\sigma$ confidence level, in all 39 cases in which the mHz QPOs disappeared at the time of an X-ray burst, the convexity of the burst is positive. The convexity measures the shape of the rising part of the burst light curve and, according to recent models, it is related to the ignition site of bursts on the neutron star surface. This finding suggests that in 4U 1636-53 these 39 bursts and the marginally-stable nuclear burning process responsible for the mHz QPOs take place at the neutron-star equator. This scenario could explain the inconsistency between the high accretion rate required for triggering mHz QPOs in theoretical models and the relatively low accretion rate derived from observations.

Accepted for publication in MNRAS; 12 pages, 3 figures

References in corpus (7)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• A catalogue of low-mass X-ray binaries in the Galaxy, LMC, and SMC (Fourth edition)
• 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
• The Latitude of Type I X-Ray Burst Ignition on Rapidly Rotating Neutron Stars
• Ignition latitude and the shape of Type I X-ray bursts
• Reaction Rate and Composition Dependence of the Stability of Thermonuclear Burning on Accreting Neutron Stars

Cited by in corpus (12)

• The Multi-INstrument Burst ARchive (MINBAR)
• Accretion disks and coronae in the X-ray flashlight
• Discovery of thermonuclear (Type I) X-ray bursts in the X-ray binary Swift J1858.6-0814 observed with NICER and NuSTAR
• Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934
• Phase-resolved analyses of mHz quasi-periodic oscillations in 4U 1636-53 using Hilbert-Huang transform
• Detection of Millihertz Quasi-Periodic Oscillations in the X-Ray Binary 1RXS J180408.9$-$342058
• Detection of millihertz quasi-periodic oscillations in the low-mass X-ray binary 4U 1730--22 with NICER
• 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
• Drifts of the marginally stable burning frequency in the X-ray binaries 4U 1608--52 and Aql X--1
• The harmonic component of the millihertz quasi-periodic oscillations in 4U 1636-53
• A solution to the tension of burning on neutron stars and nuclear physics