AAS Meeting #193 - Austin, Texas, January 1999
Session 29. Quasi-Periodic Oscillations and Pulsar Theory
Oral, Wednesday, January 6, 1999, 2:00-3:30pm, Room 9 (C)

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[29.01] Variable Frequency QPOs from the Galactic Microquasar GRS 1915+105

C. Markwardt (NASA/GSFC/NRC), J. Swank (NASA/GSFC), R. E. Taam (Northwestern U.)

The galactic ``microquasar'' GRS~1915+105 exhibits quasi-periodic oscillations (QPOs) at 67~Hz, which have been interpreted as general relativistic Lense-Thirring precession near the inner edge of an accretion disk. We report on another QPO whose frequency varies continuously from 1--15~Hz. We performed simultaneous energy and Fourier spectral analysis on RXTE PCA data from GRS~1915+105 at short intervals (e.g. 4~s). We find that the energy spectrum is well fit by a combination of an optically thick disk and power law model, and the Fourier density spectrum consists of a varying red noise component plus the variable frequency QPO. Although the energy spectrum of the QPO itself is consistent with the power law component, the properties of the QPO are most strikingly correlated with the parameters of the disk component. The QPO frequency is most tightly correlated (almost linearly) with the disk X-ray flux. In contrast, the source spectrum and variability properties are quite distinct from those observed when the 67~Hz oscillation is present.

The author(s) of this abstract have provided an email address for comments about the abstract: craigm@lheamail.gsfc.nasa.gov

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