3D Particle-in-cell Simulations of Relativistic Reconnection with Strong Synchrotron Cooling

Collisionless relativistic reconnection is believed to power high-energy emission in pulsar magnetospheres and accretion flows around black holes. The observed emission is often associated with the synchrotron radiation of leptons, accelerated in current sheets to relativistic energies. In pulsar magnetospheres, one can also expect the presence of a small fraction of heavy ions which are not affected by synchrotron losses. The dynamics of these ions in relativistic reconnection remain relatively unexplored. In this talk, I will present the results of large three-dimensional particle-in-cell simulations of isolated current sheets in different regimes of synchrotron cooling. I will discuss the structure of the 3D reconnection layer and the properties of the plasma flows in the strong radiative cooling regime. I will describe the mechanism for lepton acceleration to the Lorentz factors comparable to the magnetization parameter, and their further radiation during their encounter with the magnetic field inhomogeneities. I will also outline the acceleration channel for the uncooled ions and compare its efficiency for different regimes of lepton cooling. In particular, I show that in energetic Crab-like pulsars these ions may reach ~PeV energies. I will also demonstrate that the highest energy leptons are beamed along the upstream magnetic field. This finding provides a first-principles description of the beaming of gamma-rays produced by pulsars.