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

SDSS J134244.4+053056 is a tidal disruption event candidate with strong temporal coronal line emitters and long fading, mid-infrared dust echo. We present detailed analyses of X-ray emission from Swift/XRT observation in 2009 the most recent XMM-Newton/pn 2020. The two spectra can be modeled hard soft components. While no significant variability detected component above 2 keV between these observations, 0.3-2 varies by factor $\sim5$. luminosity this fades $\sim1.8\times10^{41}$ to $\sim3.7\times10^{40}$ erg s$^{-1}$ Swift that XMM-Newton, which are 8 19 years after outburst occurred, respectively. evolution matches $t^{-5/3}$ decline law well; there peak 10$^{44}$ at time optical flare. Furthermore, harden slightly decay phase, photon index $\Gamma$ $4.8^{+1.2}_{-0.9}$ $3.7\pm0.5$, although they consistent each other if we consider uncertainties. Additionally, comparing BH mass estimate $M-\sigma$ correlation, broad H$\alpha$ emission, fundamental plane relation accretion, find value $\sim10^{5}$Msun favored. If so, taking its spectral variation, evolution, further support theory into account, suggest long-lived lasting more than 18 an intermediate-mass black hole.