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We use 2D particle-in-cell (PIC) simulations to study the effect of thesaturated whistler instability on the viscous heating and nonthermalacceleration of electrons in a shearing, collisionless plasma with a growingmagnetic field, \textbf{B}. In this setup, an electron pressure anisotropy with$p_{\perp,e} > p_{||,e}$ naturally arises due to the adiabatic invariance ofthe electron magnetic moment ($p_{||,e}$ and $p_{\perp,e}$ are the pressuresparallel and perpendicular to \textbf{B}). If the anisotropy is large enough,the whistler instability arises, efficiently scattering the electrons andlimiting $\Delta p_e$ ($\equiv p_{\perp,e}-p_{||,e}$). In this context, $\Deltap_e$ taps into the plasma velocity shear, producing electron heating by the socalled anisotropic viscosity. In our simulations, we permanently drive thegrowth of $|\textbf{B}|$ by externally imposing a plasma shear, allowing us toself-consistently capture the long-term, saturated whistler instabilityevolution. We find that besides the viscous heating, the scattering by whistlermodes can stochastically accelerate electrons to nonthermal energies. Thisacceleration is most prominent when initially $\beta_e\sim 1$, graduallydecreasing its efficiency for larger values of $\beta_e$ ($\equiv 8\pip_e/|\textbf{B}|^2$). If initially $\beta_e \sim 1$, the final electron energydistribution can be approximately described by a thermal component, plus apower-law tail with spectral index $\sim 3.7$. In these cases, the nonthermaltail accounts for $\sim 5\%$ of the electrons, and for $\sim 15\%$ of theirkinetic energy. We discuss the implications of our results for electron heatingand acceleration in low-collisionality astrophysical environments, such aslow-luminosity accretion flows.

Stochastic Electron Acceleration by the Whistler Instability in a Growing Magnetic Field