Electron heating and acceleration by magnetic reconnection in hot accretion flows

Abstract

Both analytical and numerical works show that magnetic reconnection must occur in hot accretion flows. This process will effectively heat and accelerate electrons. In this paper we use the numerical hybrid simulation of magnetic reconnection plus test-electron method to investigate the electron acceleration and heating due to magnetic reconnection in hot accretion flows. We consider fiducial values of density, temperature, and magnetic parameter $\beta_e$ (defined as the ratio of the electron pressure to the magnetic pressure) of the accretion flow as $n_{0} \sim 10^{6} {\rm cm^{-3}}$, $T_{e}^0\sim 2\times 10^9 {\rm K}$, and $\beta_e=1$. We find that electrons are heated to a higher temperature $T_{e}=5\times 10^9$K, and a fraction $\eta\sim 8%$ of electrons are accelerated into a broken power-law distribution, $dN(\gamma)\propto \gamma^{-p}$, with $p\approx 1.5$ and 4 below and above $\sim 1$ MeV, respectively. We also investigate the effect of varying $\beta$ and $n_0$. We find that when $\beta_e$ is smaller or $n_0$ is larger, i.e, the magnetic field is stronger, $T_e$, $\eta$, and $p$ all become larger.