Hubble constant measurement from QPEs as electromagnetic counterparts to extreme mass ratio inspirals

TL;DR

This paper explores how quasi-periodic eruptions (QPEs) associated with supermassive black holes could serve as electromagnetic counterparts to gravitational wave signals from extreme mass-ratio inspirals, enabling new measurements of the Hubble constant.

Contribution

It models QPE systems under two scenarios to evaluate their detectability with LISA and their potential to constrain the Hubble constant, introducing a novel approach using QPEs as bright sirens.

Findings

No known QPEs are detectable in the stripping scenario within four years.

Two QPE sources are detectable in the orbiter-disk scenario with high signal-to-noise ratios.

Detectable QPEs could constrain the Hubble constant with fractional uncertainties below 15%.

Abstract

Gravitational waves (GWs) accompanied by electromagnetic (EM) counterparts provide a novel methodology to measure the Hubble constant ($H_0$), known as bright sirens. However, the rarity of such multi-messenger events limits the precision of the $H_0$ constraint. Recently, the newly-discovered nuclear transient, quasi-periodic eruptions (QPEs) show intriguing evidence of a stellar-mass companion captured by a supermassive black hole (SMBH) in an extreme/intermediate mass-ratio inspiral (EMRI/IMRI), which is the most promising sources of the space-based GW detectors, such as LISA. Here, we model the secular orbital evolution of known QPE systems using two frameworks: a stripping scenario in which periodic mass transfer at periapsis drives the evolution; and an orbiter-disk collision scenario in which the companion interacts with a misaligned accretion disk, modulated by coupled orbiter-disk precession. For each framework, we assess detectability by LISA, together with the resulting constraints on $H_0$. Our principal findings are: (i) in the stripping scenario, no currently known QPE reaches detectability within a four-year LISA mission. (ii) in the orbiter-disk scenario, two sources-eRO-QPE2 and eRO-QPE4-are detectable with signal-to-noise ratios $\simeq 8.5-28.8$ and constrain $H_0$ with fractional uncertainty of 6.7-14.9\%. QPE systems remain uncertain on the decade-long secular evolution. Therefore, they motivate continued time-domain monitoring of QPE candidates.