The Origin of Emission and Absorption Features in Ton S180ChandraObservations

Abstract

We present a new interpretation of the Ton S180 spectrum obtained by the Chandra Spectrometer (Low Energy Transmission Grating). Several narrow absorption lines and a few emission disk lines have been successfully fitted to the data. We have not found any significant edges accompanying line emission. We propose an interpretation of narrow lines consistent with that of the recent paper by Krolik, in which a warm absorber is strongly inhomogeneous. Such a situation is possible in the so-called multiphase medium, where regions with different ionization states, densities, and temperatures may coexist in thermal equilibrium under constant pressure. We illustrate this scenario with theoretical spectra of radiation transferred through a stratified cloud with constant pressure (instead of constant density) computed by the TITAN code in plane-parallel approximation. Detected spectral features are faint, and their presence does not alter the broadband continuum. We model the broadband continuum of Ton S180 assuming an irradiated accretion disk with a dissipative warm skin. The set of parameters appropriate for the data cannot be determined uniquely, but models with low values of the black hole mass have too hot and radially extended a warm skin to explain the formation of soft X-ray disk lines seen in the data.