Probing X-ray burst -- accretion disk interaction in low mass X-ray binaries through kilohertz quasiperiodic oscillations

Abstract

The intense radiation flux of Type I X-ray bursts is expected to interact with the accretion flow around neutron stars. High frequency quasiperiodic oscillations (kHz QPOs), observed at frequencies matching orbital frequencies at tens of gravitational radii, offer a unique probe of the innermost disk regions. In this paper, we follow the lower kHz QPOs, in response to Type I X-ray bursts, in two prototypical QPO sources, namely 4U 1636-536 and 4U 1608-522, as observed by the Proportional Counter Array of the Rossi X-ray Timing Explorer. We have selected a sample of 15 bursts for which the kHz QPO frequency can be tracked on timescales commensurable with the burst durations (tens of seconds). We find evidence that the QPOs are affected for over ~200 s during one exceptionally long burst and ~100 s during two others (although at a less significant level), while the burst emission has already decayed to a level that would enable the pre-burst QPO to be detected. On the other hand, for most of our burst-kHz QPO sample, we show that the QPO is detected as soon as the statistics allow and in the best cases, we are able to set an upper limit of ~20 s on the recovery time of the QPO. This diversity of behavior cannot be related to differences in burst peak luminosity. We discuss these results in the framework of recent findings that accretion onto the neutron star may be enhanced during Type I X-ray bursts. The subsequent disk depletion could explain the disappearance of the QPO for ~100 s, as possibly observed in two events. However, alternative scenarios would have to be invoked for explaining the short recovery timescales inferred from most bursts. Clearly the combination of fast timing and spectral information of Type I X-ray bursts holds great potential in the study of the dynamics of the inner accretion flow around neutron stars.

8 pages, 9 figures, appears in Astronomy & Astrophysics, Volume 567, id.A80, published 07/2014

References in corpus (2)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• The coherence of kHz quasi-periodic oscillations in the X-rays from accreting neutron stars

Cited by in corpus (12)

• Neutron star mass and radius measurements from atmospheric model fits to X-ray burst cooling tail spectra
• The Multi-INstrument Burst ARchive (MINBAR)
• Evidence for enhanced persistent emission during sub-Eddington thermonuclear bursts
• Observational Constraints on Neutron Star Masses and Radii
• Accretion disks and coronae in the X-ray flashlight
• The influence of accretion geometry on the spectral evolution during thermonuclear (type-I) X-ray bursts
• Determining Neutron Star Properties by Fitting Oblate-Star Waveforms To X-ray Burst Oscillations
• Insight-HXMT observations of 4U~1636-536: Corona cooling revealed with single short type-I X-ray burst
• Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR
• A state-dependent influence of the type-I bursts on the accretion in 4U 1608--52?
• Probing the accretion disc structure by the twin kHz QPOs and spins of neutron stars in LMXBs
• QPO signatures of disk restoration after type-I X-ray bursts from 4U~1636$-$536