Quasi-periodic X-ray brightness fluctuations in an accreting millisecond pulsar

R Wijnands, M van der Klis, J Homan, D Chakrabarty, C B Markwardt, E H Morgan

Research output: Contribution to journalArticlepeer-review

126 Citations (Scopus)

Abstract

The relativistic plasma flows onto neutron stars that are accreting material from stellar companions can be used to probe strong-field gravity as well as the physical conditions in the supranuclear-density interiors of neutron stars. Plasma inhomogeneities orbiting a few kilometres above the stars are observable as X-ray brightness fluctuations on the millisecond dynamical timescale of the flows(1-3). Two frequencies in the kilohertz range dominate these fluctuations: the twin kilohertz quasi-periodic oscillations (kHz QPOs). Competing models for the origins of these oscillations (based on orbital motions) all predict that they should be related to the stellar spin frequency(4-10), but tests have been difficult because the spins were not unambiguously known. Here we report the detection of kHz QPOs from a pulsar whose spin frequency is known. Our measurements establish a clear link between kHz QPOs and stellar spin, but one not predicted by any current model. A new approach to understanding kHz QPOs is now required. We suggest that a resonance between the spin and general relativistic orbital and epicyclic frequencies could provide the observed relation between QPOs and spin.

Original languageEnglish
Pages (from-to)44-47
Number of pages4
JournalNature
Volume424
Issue number6944
DOIs
Publication statusPublished - 3 Jul 2003

Keywords

  • OSCILLATION PEAK SEPARATION
  • NEUTRON-STAR
  • DIFFERENCE-FREQUENCY
  • 4U 1636-53
  • BINARIES
  • SYSTEM
  • MODEL
  • PRECESSION
  • CONSTANT
  • FIELD

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