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

Abstract

The X-ray source 3XMM~J150052.0+015452 was discovered as a spectacular tidal disruption event candidate during a prolonged ($>11$ yrs) outburst (Lin et al. 2017). It exhibited unique quasi-soft X-ray spectra of characteristic temperature $kT\sim 0.3$ keV for several years at the peak, but in a recent Chandra observation (10 yrs into the outburst) a super-soft X-ray spectrum of $kT\sim 0.15$ keV was detected. Such dramatic spectral softening could signal the transition from the super-Eddington to thermal state or the temporary presence of a warm absorber. Here we report on our study of four new XMM-Newton follow-up observations of the source. We found that they all showed super-soft spectra, suggesting that the source had remained super-soft for $>5$ yrs. Then its spectral change is best explained as due to the super-Eddington to thermal spectral state transition. The fits to the thermal state spectra suggested a smaller 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 a 0.75 msun star by a massive black hole of a few$\times 10^5$ msun. We also obtained two HST images in the F606W and F814W filters and found that the dwarf star-forming host galaxy can be resolved into a dominant disk and a smaller bulge. No central point source was clearly seen in either filter, ruling out strong optical emission associated with the X-ray activity.

9 pages, 2 figures, Accepted for publication in ApJL

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• The Rapidly Spinning Intermediate-Mass Black Hole 3XMM J150052.0+015452
• Extreme Accretion Events: TDEs and Changing-Look AGN
• LISA Constraints on an Intermediate-Mass Black Hole in the Galactic Centre
• A new X-ray tidal disruption event candidate with fast variability
• Tidal disruption events and quasi periodic eruptions
• X-ray Unveiling Events in a z~1.6 Active Galactic Nucleus in the 7 Ms Chandra Deep Field-South
• A Tidal Disruption Event from an Intermediate-mass Black Hole Revealed by Comprehensive Multi-wavelength Observations