Coherence of burst oscillations and accretion-powered pulsations in the accreting millisecond pulsar XTE J1814-338

Abstract

X-ray timing of the accretion-powered pulsations during the 2003 outburst of the accreting millisecond pulsar XTE J1814-338 has revealed variation in the pulse time of arrival residuals. These can be interpreted in several ways, including spin-down and wandering of the fuel impact point around the magnetic pole. In this Letter we show that the burst oscillations of this source are coherent with the persistent pulsations, to the level where they track all of the observed fluctuations. Only one burst, which occurs at the lowest accretion rates, shows a significant phase offset. We discuss what might lead to such rigid phase-locking between the modulations in the accretion and thermonuclear burst emission, and consider the implications for spin variation and the burst oscillation mechanism. Wandering of the fuel impact hot spot around a fixed magnetic pole seems the most likely cause for the accretion-powered pulse phase variations. This means that the burst asymmetry is coupled to the hot spot, not the magnetic pole. If premature ignition at this point (due to higher local temperatures) triggers a burning front that stalls before spreading over the entire surface, the resulting localized nuclear hot spot may explain the unusual burst and burst oscillation properties of this source.

Improvements throughout, accepted for publication in ApJ Letters

References in corpus (7)

• Timing of the Accreting Millisecond Pulsar XTE J1814-338
• Order in the Chaos: Spin-up and Spin-down during the 2002 Outburst of SAX J1808.4-3658
• Timing an Accreting Millisecond Pulsar: Measuring the Accretion Torque in IGR J00291+5934
• Spin up and phase fluctuations in the timing of the accreting millisecond pulsar XTE J1807-294
• 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
• The energy dependence of burst oscillations from the accreting millisecond pulsar XTE J1814-338

Cited by in corpus (7)

• A model for the waveform behavior of accreting millisecond pulsars: Nearly aligned magnetic fields and moving emission regions
• Constraining the Properties of the Thermonuclear Burst Oscillation Source XTE J1814-338 Through Pulse Profile Modelling
• The accretion rate dependence of burst oscillation amplitude
• Nuclear-powered X-ray millisecond pulsars
• X-ray burst ignition location on the surface of accreting X-ray pulsars: Can bursts preferentially ignite at the hotspot?
• Pulse Profile Modelling of Thermonuclear Burst Oscillations II: Handling variability
• The Peculiar Behavior of Burst Oscillations in the Accreting Millisecond X-ray Pulsar XTE J1814-338