Generation of Type I X-ray Burst Oscillations by Unstable Surface Modes

Abstract

The Rossi X-ray Timing Explorer has detected nearly coherent oscillations in the tails of type I X-ray bursts from 17 low-mass X-ray binaries. The oscillations are thought to be generated by brightness fluctuations associated with a surface mode on the rotating neutron star. The mechanism that drives the modes is, however, not understood, since the burning layer is stable to thermal perturbations. We show here via a linear perturbation analysis that, even under conditions when pure thermal perturbations are stable, nonradial surface modes may still be unstable by the epsilon mechanism. Specifically, we find that, if helium-burning reactions supply a reasonable fraction of the outgoing flux during burst decay, nonradial surface modes will grow in time. On the other hand, the same modes are likely to be stable in the presence of hydrogen burning via the rp-process. The results naturally explain why oscillations in the decay phase of type I X-ray bursts are detected only from short-duration bursts.

9 pages, accepted by ApJ

References in corpus (8)

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• The Latitude of Type I X-Ray Burst Ignition on Rapidly Rotating Neutron Stars
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• A Two-Zone Model for Type I X-ray Bursts on Accreting Neutron Stars
• Timing properties of XB 1254-690
• On the Physics of Type I X-ray Bursts on Accreting Neutron Stars at High Accretion Rates
• Hydrodynamic Thermonuclear Runaways in Superbursts
• Torsional Magnetic Oscillations in Type I X-Ray Bursts

Cited by in corpus (13)

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• Discovery of coherent millisecond X-ray pulsations in Aql X-1
• Surface Emission from Neutron Stars and Implications for the Physics of their Interiors
• Nucleosynthesis in Type I X-ray Bursts
• Systematic Uncertainties in the Spectroscopic Measurements of Neutron-Star Masses and Radii from Thermonuclear X-ray Bursts. I. Apparent Radii
• Multidimensional Modeling of Type I X-ray Bursts. I. Two-Dimensional Convection Prior to the Outburst of a Pure Helium Accretor
• NuSTAR observation of a Type I X-ray burst from GRS 1741.9-2853
• The accretion rate dependence of burst oscillation amplitude
• Relativistic ocean $r$-modes during type-I X-ray bursts
• Bursting behavior of the Galactic Center faint X-ray transient GRS 1741.9-2853
• NICER Observation of Unusual Burst Oscillations in 4U 1728-34
• Light curves from rapidly rotating neutron stars
• Damping of Type I X-ray Burst Oscillations by Convection