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The X-ray source 3XMM~J150052.0+015452 was discovered as a spectacular tidaldisruption event candidate during a prolonged ($>11$ yrs) outburst (Lin et al.2017). It exhibited unique quasi-soft X-ray spectra of characteristictemperature $kT\sim0.3$ keV for several years at the peak, but in a recentChandra observation (10 yrs into the outburst) a super-soft X-ray spectrum of$kT\sim0.15$ keV was detected. Such dramatic spectral softening could signalthe transition from the super-Eddington to thermal state or the temporarypresence of a warm absorber. Here we report on our study of four new XMM-Newtonfollow-up observations of the source. We found that they all showed super-softspectra, suggesting that the source had remained super-soft for $>5$ yrs. Thenits spectral change is best explained as due to the super-Eddington to thermalspectral state transition. The fits to the thermal state spectra suggested asmaller absorption toward the source than that obtained in Lin et al. (2017).This led us to update the modeling of the event as due to the disruption of a0.75 msun star by a massive black hole of a few$\times10^5$ msun. We alsoobtained two HST images in the F606W and F814W filters and found that the dwarfstar-forming host galaxy can be resolved into a dominant disk and a smallerbulge. No central point source was clearly seen in either filter, ruling outstrong optical emission associated with the X-ray activity.

Follow-up Observations of the Prolonged, super-Eddington, Tidal Disruption Event Candidate 3XMM~J150052.0+015452: the Slow Decline Continues