Speaker
Description
Since the 1970s, four basic solutions of the accretion flow have been discovered, namely the Shakura–Sunyaev thin disk, the Shapiro–Lightman–Eardley (SLE) solution, the slim disk, and the advection-dominated accretion flow (ADAF). Although they have achieved great success in interpreting observations in various systems, there are still some questions challenging these theoretical frameworks: i) a self-consistent unified accretion solution has not been established, ii) some observational features, e.g., the soft X-ray excess in active galactic nuclei (AGNs) and the very high state in X-ray binaries (XRBs), cannot be explained by these solutions. In this talk, I will introduce a unified description of various accretion flows and a long-ignored solution–the effectively optically thin accretion flow, which occurs at accretion rates around the Eddington value, bridging the SSD at low accretion rates and the slim disk at high rates. As a consequence of radiation-pressure dominance, the density in an SSD decreases with the increase of accretion rates, making the innermost region effectively optically thin. Further increase in accretion rate leads to a rise in the temperature so that the Compton cooling is able to balance the accretion-released energy. The effectively optically thin flow is characterized by moderate temperature and large scattering optical depth, producing a multi-colour Wien spectrum. Additionally, I will also discuss the spectrum, stability, and potential applications of this new accretion mode.
| Session Selection | Astronomy and Astrophysics |
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