Anisotropic mass ejection from black hole-neutron star binaries: Diversity of electromagnetic counterparts

TL;DR

This paper explores the anisotropic mass ejection in black hole-neutron star mergers, highlighting how it leads to diverse electromagnetic signals and unique observational features compared to neutron star mergers.

Contribution

It provides the first detailed analysis of the anisotropic ejecta's properties and their implications for electromagnetic counterparts in black hole-neutron star mergers.

Findings

Ejecta mass ranges from 0.01 to 0.1 solar masses.

Ejecta velocity is approximately 0.2c.

Ejecta exhibits significant anisotropy and directional dependence.

Abstract

The merger of black hole-neutron star binaries can eject substantial material with the mass ~0.01-0.1M_sun when the neutron star is disrupted prior to the merger. The ejecta shows significant anisotropy, and travels in a particular direction with the bulk velocity ~0.2c. This is drastically different from the binary neutron star merger, for which ejecta is nearly isotropic. Anisotropic ejecta brings electromagnetic-counterpart diversity which is unique to black hole-neutron star binaries, such as viewing-angle dependence, polarization, and proper motion. The kick velocity of the black hole, gravitational-wave memory emission, and cosmic-ray acceleration are also discussed.