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M.S. Jackson (Columbia), K.M. Leighly (U. Oklahoma), M. Matsuoka (NASDA)
ASCA observations of a broad iron K\alpha line in several Seyfert 1 nuclei suggests that the continuum reprocessing occurs quite close to the black hole. If this is true, the Compton scattering (``reflection'') component should vary along with the continuum flux. On the other hand, it is plausible that the reflection originates much farther away from the central region, for example, in the molecular torus. In this case, the reflection component should not respond to continuum changes and will be steady.
To examine the variability of the reflection component, a series of 10 simultaneous ASCA and RXTE observations with monitoring interval of ~2.5 days were made of the luminous Seyfert 1 galaxy Mrk 509 in 1996. The combination of ASCA and RXTE is particularly suited for this experiment as the softer response of ASCA constrains the power law, while the relatively harder response of RXTE allows for a fit of the reflection component parameters. Mrk 509 is a luminous Seyfert galaxy with a relatively long time scale of variability that appeared to be successfully resolved by the chosen monitoring interval.
Significant variability of both the power law index and the reflection ratio, a measure of the flux in that component relative to the power law, was observed. However, the spectral variability is complicated and interpretations in terms of the simplest geometries appear to be ruled out. In fact, an apparent hysteresis curve in the relation between the photon index of the continuum and the reflection ratio is found. This is possibly explained by a geometry where the reflecting material is relatively far away from the region which is producing the continuum, causing a delay in the reflection behind variations in the continuum. This behavior is different than has been observed in other Seyfert 1 galaxies such as NGC 5548, MCG-6-30-15, or IC 4329a.