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We perform a set of general relativistic, radiative, magneto-hydrodynamicalsimulations (GR-RMHD) to study the transition from radiatively inefficient toefficient state of accretion on a non-rotating black hole. We study ion toelectron temperature ratios ranging from $T_{\rm i}/T_{\rm e}=10$ to $100$, andsimulate flows corresponding to accretion rates as low as $10^{-6}\dot M_{\rmEdd}$, and as high as $10^{-2}\dot M_{\rm Edd}$. We have found that theradiative output of accretion flows increases with accretion rate, and that thetransition occurs earlier for hotter electrons (lower $T_{\rm i}/T_{\rm e}$ratio). At the same time, the mechanical efficiency hardly changes and accountsto ${\approx}\,3\%$ of the accreted rest mass energy flux, even at the highestsimulated accretion rates. This is particularly important for the mechanicalAGN feedback regulating massive galaxies, groups, and clusters. Comparison withrecent observations of radiative and mechanical AGN luminosities suggests thatthe ion to electron temperature ratio in the inner, collisionless accretionflow should fall within $10<T_{\rm i}/T_{\rm e}<30$, i.e., the electrontemperature should be several percent of the ion temperature.

Kinetic and radiative power from optically thin accretion flows