Rapid evolution of the recurrence time in the repeating partial tidal disruption event eRASSt J045650.3−203750
Teng Liu, Taeho Ryu, Andrew Goodwin, A. Rau, D. Homan, M. Krumpe, A. Merloni, I. Grotova, G. E. Anderson, A. Malyali, J. C. A. Miller‐Jones
Abstract
In this letter, we present the results from subsequent X-ray and UV observations of the nuclear transient eRASSt J045650.3−203750 (hereafter, J0456−20). We detected five repeating X-ray and UV flares from J0456−20, marking it as one of the most promising repeating partial tidal disruption event ( p TDE) candidates. More importantly, we also found rapid changes in the recurrence time, T recur , of the X-ray flares by modelling the long-term X-ray light curve of J0456−20. We found that T recur first decreased rapidly from about 300 days to around 230 days. It continued to decrease to around 190 days with an indication of a constant T recur , as evidenced by the latest three cycles. Our hydrodynamic simulations suggest that, in the repeating p TDE scenario, such a rapid evolution of T recur could be reproduced if the original star is a 1 M ⊙ main sequence star near the terminal age, losing nearly 80–90% of its mass during the initial encounter with a supermassive black hole (SMBH) of a mass around 10 5 M ⊙ . The inferred mass loss of 0.8–0.9 M ⊙ is higher than the estimated value of around 0.13 M ⊙ drawn from observations, which could be explained if the radiation efficiency is low (i.e. ≪0.1). Our results indicate that repeating p TDEs could be effective tools for exploring the dynamics around SMBHs beyond our own Galaxy.