A Tidal Disruption Event from an Intermediate-mass Black Hole Revealed by Comprehensive Multi-wavelength Observations

Abstract

Tidal disruption events (TDEs) occur when a star crosses the tidal radius of a black hole (BH) and is ripped apart, providing a powerful way to probe dormant BHs over a wide mass range. In this study, we present our late-time observations and comprehensive multi-wavelength analyses of AT2018cqh, a TDE at the center of a dwarf galaxy that exhibited successive flares in the optical, X-ray, and radio bands. We discovered an unexpected high-state X-ray plateau phase following the peak until the present time. Along with its reported prolonged rise lasting at least 550 days, these unique characteristics are consistent with the scenario of a TDE caused by an intermediate-mass black hole (IMBH) with a mass of approximately $(1-6) \times 10^5$ solar masses. Furthermore, scaling relations derived from the host-galaxy properties indicated a similar BH mass in concert. This discovery highlights the invaluable role of TDEs in the search for elusive IMBHs.