Abstract
We present an analysis of the X-ray variability properties of the narrow-line Seyfert 1 galaxy Ton S180, based on a 12 day continuous observation with ASCA. Examination of the light curves reveals flux variations of a factor of 3.5 in the 0.7-1.3 keV band and 3.9 in the 2-10 keV band. Time-resolved spectroscopy, using approximately daily sampling, reveals that the broad component at energies less than 2 keV shows flux variations on timescales as short as 1 day that are well correlated with the photon index and the 2-10 keV band flux. A broad Fe Kα emission is detected. There is also statistically significant evidence for a narrow Fe Kα line at ~6.8 keV, indicating an origin in ionized material. We do not detect significant variations of the Fe Kα line flux or equivalent width on timescales of ~1 day to 1 week. Despite evidence for correlated events in the power law and soft hump on timescales of a day, the flux correlations clearly do not exist on all timescales. In particular, the softness ratio reveals spectral variability on timescales as short as ~1000 s, indicating that the power-law continuum and soft hump fluxes are not well correlated on this timescale. The softness ratio also shows a slow decline across the observation, due to a combination of the different time variability of the power-law continuum and soft hump flux on timescales of ~1 week. Our timing analysis and time-selected spectroscopy indicate that the X-ray emission originates within 12 Schwarzschild radii. The amplitudes and timescales of the rapid variations that we observed are consistent with those expected within disk-corona models. Furthermore, the observed fast variability of the soft hump rules out an origin of the soft emission in large-scale components, such as circumnuclear starburst. The Γ-soft hump correlation is consistent with the soft hump being produced by upscattering of the accretion disk radiation within a patchy, flaring disk corona.
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