Variable-frequency quasi-periodic oscillations from the galactic microquasar grs 1915+105

Craig B. Markwardt*, Jean H. Swank, Ronald E. Taam

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

90 Scopus citations


We show that the galactic microquasar GRS 1915+105 exhibits quasi-periodic oscillations (QPOs) whose frequency varies continuously from 1 to 15 Hz during spectrally hard dips when the source is in a flaring state. We report here analyses of simultaneous energy spectra and power density spectra at 4 s intervals. The energy spectrum is well fit at each time step by an optically thick accretion disk plus power-law model, while the power density spectrum consists of a varying red noise component plus the variable-frequency QPO. The features of both spectra are strongly correlated with one another. The 1-15 Hz QPOs appear when the power-law component becomes hard and intense and themselves have an energy spectrum consistent with the power-law component (with rms amplitudes as high as 10%). The frequency of the oscillations, however, is most strikingly correlated with the parameters of the thermal disk component. The tightest correlation is between QPO frequency and disk X-ray flux. This fact indicates that the properties of the QPO are not determined solely by a disk or solely by a corona.

Original languageEnglish (US)
Pages (from-to)L37-L40
JournalAstrophysical Journal
Issue number1 PART 2
StatePublished - Mar 1 1999


  • Accretion, accretion disks
  • Black hole physics
  • Stars: oscillations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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