Hot one-temperature accretion flows revisited

The effectiveness of the thermal coupling of ions and electrons in the context of optically thin, hot accretion flows is investigated in a phenomenological approach. In the limit of complete coupling, we focus on the one-temperature accretion flows around black holes. Based on a global analysis, the results are compared with two-temperature accretion flow models and with the observations of black hole sources. A comparison of the properties of the one-temperature solutions with that of the two-temperature solutions reveals many features that are quite similar. That is, hot one-temperature solutions are found to exist for mass flow rates less than a critical value; i.e., Ṁ . 10αṀEdd, where ṀEdd = LEdd/c 2 is the Eddington accretion rate. At low mass flow rates, Ṁ . 10αṀEdd, the viscous energy is mainly balanced by the advective cooling, i.e., the solution is in the advection-dominated accretion flow (ADAF) regime. On the other hand, at higher rates, 10αṀEdd . Ṁ . 10α ṀEdd, radiative cooling is effective and is mainly balanced by advective heating, placing the solution in the regime of luminous hot accretion flow (LHAF). At the highest mass flow rates, Ṁ & 10αṀEdd,