Impact of a mean field dynamo on jet and wind launching from neutron-star merger remnants

We present a mean field model for the αΩ-dynamo potentially active in the post-merger phase of a binary neutron star coalescence. We introduce simplified equations for ideal general relativistic magnetohydrodynamics (GRMHD) with an additional α−term, which closely resemble their Newtonian counterpart, but remain compatible with standard numerical relativity simulations. We propose a heuristic dynamo closure relation for the magnetorotational instability-driven turbulent dynamo in the outer layers of a differentially rotating magnetar remnant and its accretion disk. We demonstrate that depending on the strength of the dynamo action, magnetically driven outflows from the magnetar remnant can be present with their amount of baryon loading correlating with the magnetic field amplification. Our results are consistent with the expectation that substantial dynamo amplification (either during or after the merger) may be required for neutron-star remnants to power short gamma-ray bursts or precursors thereof. Finally, we provide an outlook into the subsequent evolution of the system, including novel radiative gamma-ray burst signatures.