Ideal E/IMRI vs Real E/IMRI system : Observable signature in LISA

TL;DR

This paper investigates how accretion disks around supermassive black holes in real E/IMRI systems affect gravitational wave signals detectable by LISA, providing insights into accretion physics and system properties.

Contribution

It introduces a semi-relativistic model to analyze the impact of accretion disks on GW signals from E/IMRIs, highlighting the potential for LISA to probe accretion flow characteristics.

Findings

Disk-induced waveform modifications are detectable within six months of observation.

Detectability depends on accretion rate and system distance, with significant effects for systems within 3 Gpc.

Observations can help distinguish different accretion flow models.

Abstract

Real extreme/intermediate mass ratio inspiral(E/IMRI) systems are likely to contain large accretion disks which could be as massive as the central supermassive black hole. Therefore, contrary to its ideal model, a real E/IMRI system contains a third important component: the accretion disk. We study the influence of these disks on the emitted GW profile and its detectability through proposed LISA observation. We use a semi-relativistic formalism in the Kerr background (Gair & Glampedakis 2006; Barausse & Rezzolla 2008) for the case of transonic accretion flow which is a potential candidate to describe the accretion flows around AGN. The hydrodynamic drag of the disks modified the motion of the companion as a result the emitted wave changes in amplitude and phase. We found that these changes are detectable through the last few years of observation by LISA (in some cases as small as six months) for EMRIs residing within 3 GPc from the detector and for the accretion rate of the primary black hole of the order of $\dot{M}=1 \dot{M}_{Edd}$. These choices of parameter values are consistent with real systems. The drag effect and hence the detectability of the emitted GW is sensitive to the hydrodynamical model of the disk. Therefore such observations will help one to identify the nature of the accretion flow and verify various paradigms of accretion physics.