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SDSS J134244.4+053056 is a tidal disruption event candidate with strongtemporal coronal line emitters and a long fading, mid-infrared dust echo. Wepresent detailed analyses of X-ray emission from a Swift/XRT observation in2009 and the most recent XMM-Newton/pn observation in 2020. The two spectra canbe modeled with hard and soft components. While no significant variability isdetected in the hard component above 2 keV between these two observations, thesoft X-ray emission in 0.3-2 keV varies by a factor of $\sim5$. The luminosityof this soft component fades from $\sim1.8\times10^{41}$ to$\sim3.7\times10^{40}$ erg s$^{-1}$ from the observation in Swift to that ofXMM-Newton, which are 8 and 19 years after the outburst occurred, respectively.The evolution of luminosity matches with the $t^{-5/3}$ decline law well; thereis a soft X-ray peak luminosity of 10$^{44}$ erg s$^{-1}$ at the time of theoptical flare. Furthermore, the spectra of the soft component harden slightlyin the decay phase, in which the photon index $\Gamma$ varies from$4.8^{+1.2}_{-0.9}$ to $3.7\pm0.5$, although they are consistent with eachother if we consider the uncertainties. Additionally, by comparing the BH massestimate between the $M-\sigma$ correlation, the broad H$\alpha$ emission, andthe fundamental plane relation of BH accretion, we find that a value of$\sim10^{5}$Msun is favored. If so, taking its X-ray spectral variation,luminosity evolution, and further support from theory into account, we suggestthat SDSS J134244.4+053056 is a long-lived tidal disruption event candidatelasting more than 18 years with an intermediate-mass black hole.

Long-term X-ray evolution of SDSS J134244.4+053056.1: A more than 18 year-old, long-lived IMBH-TDE candidate