HLX-1 as a Repeating Partial Tidal Disruption Event around an Intermediate-Mass Black Hole

ESO 243$-$49 HLX–1 is one of the first known compelling intermediate-mass black hole (IMBH) candidates, but the origin of its recurrent X-ray outbursts remains unsettled. In this work we fit the HLX–1 outbursts simultaneously with a relativistic thin-disk time-dependent model. The black-hole and disk-geometry parameters are tied across epochs, while the injected mass and timing parameters are fitted separately for each outburst. We also include a contemporaneous $\mathit{\text{HST}}$ UV/optical/IR spectral energy distribution obtained near the peak of one outburst, which constrains the global temperature and radius scales of the disk. The soft-state data are consistent with a common global solution, with black hole mass ${\log }_{10}(M_{\bullet }\mathrm{/}{M}_{\odot })=4.5\pm 0.2$ and disk formation radius ${\log }_{10}(r_0\mathrm{/}{r}_g)=3.8\pm 0.3$. The differences between outbursts are mainly described by modest changes in disk mass and viscous timescales. The inferred injected masses are typically $\sim {10}^{-3}{M}_{\odot }$ per outburst, requiring a total fuel supply of at least a few $\times {10}^{-3}{M}_{\odot }$ across the observed sequence. This mass scale, and the disk size, are consistent with repeated partial stripping of a low-mass donor. A simple Keplerian mapping of the flare gaps and fitted disk radius implies a highly eccentric orbit with a pericenter just outside the donor’s tidal radius. These results support a repeating partial tidal disruption interpretation for the origin of HLX–1.