Fast Radio Bursts and Radio Transients from Black Hole Batteries

TL;DR

This paper proposes that black hole-neutron star mergers produce radio transients resembling fast radio bursts, with distinctive double-peak signals, offering a new electromagnetic counterpart for gravitational wave detections and insights into neutron star magnetic fields.

Contribution

It introduces a novel model where black hole-neutron star interactions generate radio bursts with unique double-peak features, expanding the potential sources and observational signatures of FRBs.

Findings

Proposes a double-peak radio transient signature from BH-NS mergers.

Suggests these transients can serve as electromagnetic counterparts to GW signals.

Highlights the potential to study NS magnetic fields through these events.

Abstract

Most black holes (BHs) will absorb a neutron star (NS) companion fully intact, without tidal disruption, suggesting the pair will remain dark to telescopes. Even without tidal disruption, electromagnetic luminosity is generated from the battery phase of the binary when the BH interacts with the NS magnetic field. Originally the luminosity was expected in high-energy X-rays or gamma-rays, however we conjecture that some of the battery power is emitted in the radio bandwidth. While the luminosity and timescale are suggestive of fast radio bursts (FRBs; millisecond-scale radio transients) NS--BH coalescence rates are too low to make these a primary FRB source. Instead, we propose the transients form a FRB sub-population, distinguishable by a double peak with a precursor. The rapid ramp-up in luminosity manifests as a precursor to the burst which is $20\%-80\%$ as luminous, given 0.5~ms timing resolution. The main burst is from the peak luminosity before merger. The post-merger burst follows from the NS magnetic field migration to the BH, causing a shock. NS--BH pairs are especially desirable for ground-based gravitational wave (GW) observatories since the pair might not otherwise be detected, with electromagnetic counterparts greatly augmenting the scientific leverage beyond the GW signal. Valuably, the electromagnetic signal can break degeneracies in the parameters encoded in the GW as well as probe the NS magnetic field strength, yielding insights into open problems in NS magnetic field decay.