Radiative efficiency of hot accretion flow

• 作 者: FU-GUOXIE;
• 出 处: 国际天文学联合会第312次专题会议
• 发表日期: 2014年期

　　Our understanding of hot accretion flows has been improved significantly by two findings over the recent years:(i)only a small fraction of the accretion flow available at the outer boundary can finally fall on to the black hole,while most of it is lost in the outflow;(ii)electrons can directly receive a large fraction of the viscously dissipated energy in the accretion flow(i.e.δ~0.1–0.5).The radiative efficiency of the hot accretion flow when these two findings are taken into account has not yet been systematically studied,and will be discussed in this talk.We consider two regimes of the hot accretion model: advectiondominated accretion flows that lie in the regime of the low accretion rate,and the luminous hot accretion flows(LHAFs)that lie above certain accretion rate.For the LHAFs,we assume that the accretion flow has a two-phase structure above a certain accretion rate,and we adopt a simplification in our calculation of the dynamics.Our results indicate that the radiative efficiency of hot accretion flow increases with the accretion rate and that it is greatly enhanced by the direct viscous heating to electrons,compared to the previous case of δ(《)1.When the accretion rate is high,the radiative efficiency of the hot accretion flow is comparable to that of a standard thin disc.Applications are also addressed,e.g.the consequences on the radio–X-ray correlation observed in the hard states of black hole X-ray binaries.