Partial tidal disruption events by intermediate-mass black holes in supermassive and intermediate-mass black hole binaries

Abstract

ABSTRACT In the centres of galaxies, stars that orbit supermassive black hole binaries (SMBHBs) can undergo tidal disruptions due to the Lidov–Kozai mechanism. Nevertheless, most previous researches have predominantly focused on full tidal disruption events (FTDEs). In this study, we employ N-body simulations to investigate partial tidal disruption events (PTDEs) induced by intermediate-mass black holes (IMBHs) in SMBH–IMBH binaries, taking into account consideration the IMBH’s mass, semimajor axis, and eccentricity of the outer orbit. Our findings indicate that, in comparison to FTDEs, the majority of tidal disruption events are actually PTDEs. Furthermore, we find that a significant number of stars experiencing partial disruption ultimately get captured by the IMBH, potentially leading to repeating flares. By comparing the period of the periodic eruptions observed in ASASSN-14ko, we find that PTDEs in a specific SMBH–IMBH binary system can align with the observed period if the SMBH has a mass of $10^7\rm {\ M_\odot }$, the IMBH has a mass smaller than approximately $10^5\rm {\ M_\odot }$, the eccentricity of the SMBH–IMBH binary exceeds approximately 0.5, and the semimajor axis of the SMBH–IMBH binary is larger than approximately 0.001 pc. Moreover, our model effectively accounts for the observed period derivative for ASASSN-14ko ($\dot{P}=-0.0026\pm 0.0006$), and our results also imply that some quasi-periodic eruptions may be attributed to PTDEs occurring around SMBH–IMBH binaries.