Long-term X-ray evolution of SDSS J134244.4+053056.1

A more than 18 year-old, long-lived IMBH-TDE candidate

¹ Department of Astronomy, Guangzhou University, Guangzhou 510006, PR China
e-mail: doulm@gzhu.edu.cn
² College of Engineering Physics, Shenzhen Technology University, Shenzhen 518118, PR China
³ Department of Physics, Anhui Normal University, Wuhu, Anhui 241000, PR China
⁴ CAS Key Laboratory for Researches in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026, PR China
⁵ School of Physics and Astronomy, Sun Yat-Sen University, Zhuhai 519082, PR China
⁶ Shenzhen Key Laboratory of Ultraintense Laser and Advanced Material Technology, Shenzhen 518118, PR China

Received: 18 March 2021
Accepted: 21 May 2021

Abstract

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 ∼5. The luminosity of this soft component fades from ∼1.8 × 10⁴¹ to ∼3.7 × 10⁴⁰ 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^−5/3decline law well; there is a soft X-ray peak luminosity of 10⁴⁴ 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 Γ 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 − σ correlation, the broad Hα emission, and the fundamental plane relation of BH accretion, we find that a value of ∼10⁵ M_⊙ 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.