Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-08-06
Astrophys.J.564:162-175,2002
Astronomy and Astrophysics
Astrophysics
11 pages, 9 figures; accepted for publication in The Astrophysical Journal, LaTeX emulateapj.sty
Scientific paper
10.1086/324201
We present an analysis of the X-ray variability properties of the NLS1 galaxy Ton S180, based upon a 12-day continuous ASCA observation. We observe 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 (~1d sampling) reveals that the broad `soft hump' component at energies <2 keV shows flux variations on timescales down to 1 day that are well correlated with the photon index and the 2-10 keV band flux. A broad Fe K$\alpha$ emission is detected. There is a evidence for a narrow Fe K$\alpha$ line at ~6.8 keV, indicating an origin in ionized material. We do not detect significant variations of the line flux or EW on ~1 day-1 week timescales. The softness ratio reveals spectral variability on timescales down to ~1000 s, indicating that the power-law continuum and soft hump fluxes are not well correlated on this timescale. It 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. The X-ray emission originates within 12 Schwarzschild radii, and the amplitudes and timescales of the rapid variations we observed are consistent with those expected within disk-corona models. The soft hump variability timescale rules out an origin in large scale components (circumnuclear starburst). The $\Gamma$-soft hump correlation is consistent with the soft hump being produced by up-scattering of the accretion disk radiation within a flaring disk corona.
George Ian Michael
Mathur Savita
Romano Pado
Turner Tracey Jane
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