Pre-merger electromagnetic counterparts of binary compact stars

TL;DR

This paper explores electromagnetic signals from binary compact star mergers, predicting observable signatures like synchrotron radiation, blackbody emission, and potential fast radio bursts as precursors to gravitational wave events.

Contribution

It introduces a detailed model of electromagnetic emissions, including synchrotron and blackbody components, as precursors to gravitational wave signals from magnetized compact star mergers.

Findings

Electromagnetic power can reach 10^{38} - 10^{44} erg/s before merger.

Synchrotron radiation can produce GeV to MeV energies depending on binary type.

Blackbody emission peaks at keV to hundreds of keV energies, with distinguishable modulation patterns.

Abstract

We investigate emission signatures of binary compact star gravitational wave sources consisting of strongly magnetized neutron stars (NSs) and/or white dwarfs (WDs) in their late-time inspiral phase. Because of electromagnetic interactions between the magnetospheres of the two compact stars, a substantial amount of energy will be extracted, and the resultant power is expected to be $\sim 10^{38} - 10^{44}$ erg/s in the last few seconds before the two stars merge, when the binary system contains a NS with a surface magnetic field $10^{12}$ G. The induced electric field in the process can accelerate charged particles up to the EeV energy range. Synchrotron radiation is emitted from energetic electrons, with radiative energies reaching the GeV energy for binary NSs and the MeV energy for NS - WD or double WD binaries. In addition, a blackbody component is also presented and it peaks at several to hundreds keV for binary NSs and at several keV for NS - WD or double WD binaries. The strong angular dependence of the synchrotron radiation and the isotropic nature of the blackbody radiation lead to distinguishable modulation patterns between the two emission components. If coherent curvature radiation is presented, fast radio bursts could be produced. These components provide unique simultaneous electromagnetic signatures as precursors of gravitational wave events associated with magnetized compact star mergers and short gamma ray bursts (e.g., GRB 100717).