Constraints on the maximum mass of neutron stars from gravitational wave events and prospects for electromagnetic precursor emission from inspiralling neutron star binaries

Since the first detection of a gravitational wave event of the merger of two neutron stars in 2017, two more detections in the neutron star mass range have been announced.  The first one, GW190425, involved an unusually massive neutron star, the second one, GW190814, had a companion in the lower mass gap that could either have been the heaviest neutron star or the lightest black hole ever observed. Based on constraints on the neutron star maximum mass derived in the context of GW170817, I will discuss the possibility of having a very massive neutron star in the GW190814 event and its implications for the neutron star equation of state.

In the second half of the talk, I will discuss a scenario for the production of electromagnetic precursor emission in the late neutron star inspiral. Since neutron stars are equipped with strong magnetic fields, the non-trivial interaction of two neutron star magnetospheres before the merger might give rise to an electromagnetic precursor emission. I will present a mechanism for launching powerful electromagnetic flares during the inspiral of two neutron stars.  Using special-relativistic force-free electrodynamics simulations, I will demonstrate that differential motion, such as relative spin differences between the neutron stars or misalignment of the magnetic field with the orbital axis, can naturally lead to a periodic emission of such flares. I will also comment on the viability to produce radio emission in this process.