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Rapid gamma-ray flares pose an astrophysical puzzle, requiring mechanismsboth to accelerate energetic particles and to produce fast observedvariability. These dual requirements may be satisfied by collisionlessrelativistic magnetic reconnection. On the one hand, relativistic reconnectioncan energize gamma-ray emitting electrons. On the other, as previous kineticsimulations have shown, the reconnection acceleration mechanism preferentiallyfocuses high-energy particles -- and their emitted photons -- into beams, whichmay create rapid blips in flux as they cross a telescope's line of sight. Usinga series of 2D pair-plasma particle-in-cell simulations, we explicitlydemonstrate the critical role played by radiative cooling in mediating theobservable signatures of this `kinetic beaming' effect. Only in our efficientlycooled simulations do we measure kinetic beaming beyond one light crossing timeof the reconnection layer. We find a correlation between the cooling strengthand the photon energy range across which persistent kinetic beaming occurs:stronger cooling coincides with a wider range of beamed photon energies. Wealso apply our results to rapid gamma-ray flares in flat-spectrum radioquasars, suggesting that a paradigm of radiatively efficient kinetic beamingconstrains relevant emission models. In particular, beaming-producedvariability may be more easily realized in two-zone (e.g. spine-sheath)set-ups, with Compton seed photons originating in the jet itself, rather thanin one-zone external Compton scenarios.

Kinetic Beaming in Radiative Relativistic Magnetic Reconnection: A Mechanism for Rapid Gamma-Ray Flares in Jets