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[91.05] The Compton Microscope: Using the Energy Dependence of QPO Amplitudes to Probe Their Origin in Accretion Disks

D.E. Lehr, R.V. Wagoner (Stanford Univ.), J. Wilms (Inst. für Astronomie und Astrophysik, Tübingen, Germany)

We report the development of a new tool to determine the origin of quasi-periodic oscillations (QPOs) in accretion disk systems. The technique uses the source energy spectrum and the energy dependence of the QPO fractional amplitude to restrict the location of the emission region of the modulated photons, which are assumed to originate in the inner accretion disk. Both Monte-Carlo and semi-analytical methods are presented. We assume the accretion disk is enshrouded by a slab atmosphere of hot electrons in which unsaturated Compton scattering produces the high-energy spectrum. Properties of the atmosphere, in particular the electron temperature, are assumed functions of radius from the central compact object. We show that our model reproduces the observed energy dependence of the fractional amplitude of the 67 Hz QPO in GRS 1915+105 if the QPO is assumed to originate at a particular region of the inner disk.

This work was supported by NASA Graduate Student Researchers Program grant NGT 5-50044 to D.E.L., NASA grant NAG 5-3102 to R.V.W., and grant number Sta 173/22 of the Deutsche Forschungsgemeinschaft to J.W. This research has made use of data obtained through the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center.