Electromagnetic Precursors to Gravitational-wave Events: Numerical Simulations of Flaring in Pre-merger Binary Neutron Star Magnetospheres

Abstract

The detection of gravitational waves from neutron star merger events has opened up a new field of multi-messenger astronomy linking gravitional waves events to short-gamma ray bursts and kilonova afterglows. A further -yet to be discovered -electromagnetic counterpart is precursor emission produced by the non-trivial interaction of the magnetospheres of the two neutron stars prior to merger. By performing special-relativistic force-free simulations of orbiting neutron stars we discuss the effect of different magnetic field orientations and show how the emission can be significantly enhanced by differential motion present in the binary, either due to stellar spins or misaligned stellar magnetospheres. We find that the build-up of twist in the magnetic flux tube connecting the two stars can lead to the repeated emission of powerful flares for a variety of orbital configurations. We also discuss potential coherent radio emission mechanisms in the flaring process.

Electromagnetic Precursors of Short Gamma-Ray Bursts as Counterparts of Gravitational Waves

“…Note that, here and below, we adopt the approximation of Ω Ω * , this is appropriate, as we are considering the last few seconds before the merger. Simulations of inspiraling NS-NS/BH binaries indicate that the main features are well captured by this model (e.g., [58,59,61,63,71,72]). The other cases are more complicated.…”

“…We noticed that, for real cases, the magnetic axis may have an inclination angle with respect to the orbital axis, and in these cases, the energy dissipation rate would lie in between the above scenarios. As the poloidal field is the dominant component, we ignored the contribution of the toroidal magnetic field, which are caused by the revolution of the binary system and are observed in many simulations (e.g., [58,59,61,63,71,72]).…”

“…Besides, there are two more scenarios proposed only for SGRB precursors. During the inspiral phase of the NS-NS/black hole (BH) binary, the magnetospheric interaction of the binary [55][56][57][58][59][60][61][62][63], or the crust crack of the NS [64][65][66] may also generate gamma-ray emissions. As such, precursors of SGRBs may shed light on the physical processes right before or shortly after the merger.…”

Electromagnetic counterparts of compact binary mergers

“…The problem has been studied also with general relativistic resistive MHD (Palenzuela et al 2013), special relativistic (Sridhar et al 2020), force-free (Most & Philippov 2020) and particles-in-cell (Crinquand, Cerutti & Dubus 2019) simulations. These works allow us to appreciate the important role of magnetic reconnection in accelerating particles, which can further contribute to the emission.…”

Early warning of coalescing neutron-star and neutron-star-black-hole binaries from the nonstationary noise background using neural networks

“…The property of the final merger product may be better revealed with prompt X-ray and optical observations [24]. In the radio band, precursor magnetosphere interactions might cause radio emissions [25,26] and could be a potential mechanism leading to fast radio bursts [27,28]. See, e.g., Ref.…”