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 candidates, but the origin of its recurrent X-ray outbursts has remained unsettled.

In this work, the authors 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. They also include a contemporaneous Hubble Space Telescope 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, yielding a black hole mass of log10(M_BH/M_sun) = 4.5 +/- 0.2 and a disk formation radius of log10(r0/r_g) = 3.8 +/- 0.3. Differences between outbursts are mainly described by modest changes in disk mass and viscous timescales. The inferred injected masses are typically about 10^-3 solar masses per outburst, requiring a total fuel supply of at least a few times 10^-3 solar masses 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 the 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.