No abstract

The successful joint observation of the gravitational wave event GW170817 and its multi-wavelength electromagnetic counterparts first enables human to witness a definite merger event of two neutron stars (NSs). This historical event confirms the origin of short-duration gamma-ray bursts (GRBs), and in particular, identifies the theoretically-predicted kilonova phenomenon that is powered by radioactive decays of r-process heavy elements. However, whether a long-lived remnant NS could be formed during this merger event remains unknown, although such a central engine has been suggested by afterglow observations of some short-duration GRBs. By invoking this long-lived remnant NS, we here propose a model of hybrid energy sources for the kilonova AT2017gfo associated with GW 170817. While the early emission of AT2017gfo is still powered radioactively as usually suggested, its late emission is primarily caused by delayed energy injection from the remnant NS. In our model, only one single opacity is required and an intermediate value of κ ≃ 0.97 cm 2 g −1 is revealed, which could be naturally provided by lanthanide-rich ejecta that is deeply ionized by the emission from a wind of the NS. These self-consistent results indicate that a long-lived remnant NS, which must own a very stiff equation of state, had been formed during the merger event of GW170817. This provides a very stringent constraint on the strong interaction in nuclear-quark matter. It is further implied that such GW events could provide a probe of the early spin and magnetic evolutions of NSs, e.g., the burying of surface magnetic fields.

In this Letter, we propose that a fast radio burst (FRB) could originate from the magnetic interaction between double neutron stars (NSs) during their final inspiral within the framework of a unipolar inductor model. In this model, an electromotive force is induced on one NS to accelerate electrons to an ultra-relativistic speed instantaneously. We show that coherent curvature radiation from these electrons moving along magnetic field lines in the magnetosphere of the other NS is responsible for the observed FRB signal, that is, the characteristic emission frequency, luminosity, duration, and event rate of FRBs can be well understood. In addition, we discuss several implications of this model, including double-peaked FRBs and possible associations of FRBs with short-duration gamma-ray bursts and gravitational-wave events.