Discovery of Millihertz ULTRAVIOLET Quasi-periodic Oscillations in Hercules X-1

B Boroson, K O'Brien, Keith Douglas Horne, T Kallman, M Still, PT Boyd, H Quaintrell, SD Vrtilek

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17 Citations (Scopus)

Abstract

Observations of the ultraviolet continuum of the X-ray binary system Her X-1/HZ Herculis with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST) show quasi-periodic oscillations (QPOs) at frequencies of 8 +/- 2 and 43 +/- 2 mHz, with rms amplitudes of 2% and 4% of the steady flux. Observations with the Keck Telescope confirm the presence of the higher frequency QPO in the optical continuum, with a rms amplitude of 1.6% +/- 0.2%. The QPOs are most prominent in the HST data near phi =0.5 (where phi =0 is the middle of the X-ray eclipse), suggesting that they arise not in the accretion disk but on the X-ray-heated face of the companion star. We discuss scenarios in which the companion star reprocesses oscillations in the disk which are caused by either Keplerian rotation or a beat frequency between the neutron star spin and Keplerian rotation at some radius in the accretion disk.

Original languageEnglish
Pages (from-to)pp.399-406.
Number of pages8
JournalAstrophysical Journal
Volume545
Issue number1
Publication statusPublished - 10 Dec 2000

Keywords

  • binaries : close
  • stars : individual (HZ Herculis)
  • stars : oscillations
  • ultraviolet : stars
  • X-rays : stars
  • TELESCOPE IMAGING SPECTROGRAPH
  • HZ HERCULIS
  • NEUTRON-STAR
  • 4U 1626-67
  • X-1
  • PULSAR
  • MASS
  • PULSATIONS
  • ACCRETION
  • SPECTRUM

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