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The long-term Swift monitoring of ESO 243-49 HLX-1 provides an opportunity toinvestigate the detailed timing and spectral behaviour of this hyper-luminousX-ray source. Swift has detected 7 outbursts since 2009 mid-August. Usingdifferent dynamical timing algorithms, we confirm an increasing trend for thetime intervals between outbursts, which is manifest in the delays between thelatest outbursts. The X-ray spectra of HLX-1 in quiescence can be describedwith a single power-law model while the thermal component dominates the X-rayemission during outburst. There is only marginal evidence for photon index (orspectral hardness) changes between quiescent states with about 1{\sigma}deviation. With the updated temporal and spectral features, we re-examinedifferent scenarios to explain the origin of the quasi-periodic modulation ofHLX-1. A significantly increasing trend without obvious stochastic fluctuationson the timescale of the detected quasi-period may not fully support an orbitalperiod origin as might be due to mass transfer episodes from a donor star atperiastron of an extremely eccentric orbit. The outburst profile seems to beconsistent with the effect of tidal-induced-precession of an accretion disc oran oscillating wind scenario in the inner disc. Based on these models, wespeculate that the true orbital period is much shorter than the detectedquasi-periodicity.

Investigation of X-ray timing and spectral properties of ESO 243-49 HLX-1 with long-term Swift Monitoring