Fast Radio Bursts: Electromagnetic Counterparts to Extreme Mass Ratio Inspirals

TL;DR

This paper explores the potential of fast radio bursts (FRBs) as electromagnetic counterparts to extreme mass ratio inspirals (EMRIs), linking radio observations with gravitational wave signals to enhance understanding of cosmic phenomena and cosmology.

Contribution

It introduces the idea that FRBs associated with SMBH-NS systems can serve as EM counterparts to EMRIs, enabling multi-messenger observations and cosmological measurements.

Findings

EMRI signals from SMBH-NS systems detectable up to z~0.04 by LISA and Tianqin.

Event rate of such FRB-EMRI systems can be as high as 1 Gpc$^{-3}$ yr$^{-1}$.

FRB-EMRI associations can help identify FRB progenitors and serve as standard sirens for cosmology.

Abstract

Recent observations discovered that some repeating fast radio bursts (FRBs) show a large value and complex variations of Faraday rotation measures (RMs). The binary systems containing a supermassive black hole (SMBH) and a neutron star (NS) can be used to explain such RM variations. Meanwhile, such systems produce low-frequency gravitational wave (GW) signals, which are one of the primary interests of three proposed space-based GW detectors: the Laser Interferometer Space Antenna (LISA), Tianqin and Taiji. These signals are known as extreme mass ratio inspirals (EMRIs). Therefore, FRBs can serve as candidates of electromagnetic (EM) counterparts for EMRI signals. In this letter, we study the EMRI signals in this binary system, which can be detected up to $z\sim0.04$ by LISA and Tianqin for the most optimistic case. Assuming the cosmic comb model for FRB production, the total event rate can be as high as $\sim1$ Gpc$^{-3}$ yr$^{-1}$. EMRI signals associated with FRBs can be used to reveal the progenitor of FRBs. It is also a new type of standard siren, which can be used as an independent cosmological probe.