Zhumao Zhang, Xinwen Shu, Lei Yang, Luming Sun, Hucheng Ding, Lin Yan, Ning Jiang, Fangxia An, Walter Silima, Fabao Zhang, Yogesh Chandola, ZhongZu Wu, DaiZhong Liu, Liming Dou, Jianguo Wang, Yibo Wang, Chenwei Yang, Di Li, Tianyao Zhou, Wenjie Zhang, Fangkun Peng, Tinggui Wang
Abstract SDSS J1115+0544 is a unique low-ionization nuclear emission-line region galaxy with energetic ultraviolet (UV), optical, and mid-infrared outbursts occurring in its nucleus. We present the results from an analysis of multiwavelength photometric and radio follow-up observations with a time span of ≈9 yr since its discovery. We find that following a luminosity plateau of ≈500 days, the UV/optical emission has decayed back to the preoutburst level, suggesting that the nuclear outburst might be caused by a stellar tidal disruption event (TDE). In this case, J1115+0544 could be an unusually slowly evolving optical TDE with longest rise and decline time scales ever found. Three years later than the optical peak, a delayed radio brightening was found with a luminosity as high as νL ν (5.5 GHz) ∼ 1.9 × 10 39 erg s −1 . Using a standard equipartition analysis, we find that the outflow powering the radio emission was launched at t ≳ 1150 days with a velocity of v ≲ 0.1 c and a minimal kinetic energy of E K ≳ 3 × 10 49 erg. The delayed radio brightening coupled with the disappearing plateau in the UV/optical light curves is consistent with the scenario involving delayed ejection of an outflow from a state transition in the disk. SDSS J1115+0544 is the first TDE candidate displaying both a short-lived UV/optical plateau emission and a late-time radio brightening. Future radio observations of these TDEs in the postplateau decay phase will help to establish the connection between outflow launching and changes in accretion rate.