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 a long fading, mid-infrared dust echo. We present detailed analyses of X-ray emission from a Swift/XRT observation in 2009 and the most recent XMM-Newton/pn observation in 2020. The two spectra can be modeled with hard and soft components. While no significant variability is detected in the hard component above 2 keV between these two observations, the soft X-ray emission in 0.3-2 keV varies by a factor of similar to 5. The luminosity of this soft component fades from similar to 1.8 x 10(41) to similar to 3.7 x 10(40) erg s(-1) from the observation in Swift to that of XMM-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; there is a soft X-ray peak luminosity of 10(44) erg s(-1) at the time of the optical flare. Furthermore, the spectra of the soft component harden slightly in the decay phase, in which the photon index Gamma varies from 4.8(-0.9)(+1.2) to 3.7 +/- 0.5, although they are consistent with each other if we consider the uncertainties. Additionally, by comparing the BH mass estimate between the M - sigma correlation, the broad H alpha emission, and the fundamental plane relation of BH accretion, we find that a value of similar to 10(5)M(circle dot) is favored. If so, taking its X-ray spectral variation, luminosity evolution, and further support from theory into account, we suggest that SDSS J134244.4+053056 is a long-lived tidal disruption event candidate lasting more than 18 years with an intermediate-mass black hole.

Automated summary

SDSS J134244.4+053056 is a tidal disruption event candidate with strong temporal coronal line emitters and a long fading, mid-infrared dust echo. Detailed analyses of X-ray emission from Swift/XRT and XMM-Newton/pn observations in 2009 and 2020 reveal that the soft X-ray emission varies significantly while the hard component remains stable. The luminosity evolution of the soft component follows the t(-5/3) decline law, with a peak luminosity at the time of the optical flare. Spectral hardening of the soft component is also observed during the decay phase. Furthermore, comparisons of various black hole mass estimates suggest a value of about 10(5) solar masses, indicating the presence of an intermediate-mass black hole in SDSS J134244.4+053056.