Researchers reveal unique tidal disruption event with apparent early optical collision

A research team from the Chinese Academy of Sciences (CAS) University of Science and Technology of China (USTC) conducted a detailed analysis of a tidal disruption event (TDE) with unique characteristics, providing new insights into the behavior of TDEs and their impacts.The study was published online in Astrophysical Journal Communications.

When a star gets too close to the supermassive black hole at the center of a galaxy, it gets ripped apart by the black hole’s massive tidal forces, causing a phenomenon called tidal bulge.

Researchers found that the AT2023lli event observed by various ground and space telescopes, including the newly built Wide Field Survey Telescope (WFST) jointly operated by the University of Science and Technology of China and the Purple Mountain Observatory of the Chinese Academy of Sciences, showed unique characteristics that were different from previous TDEs. Traditionally, TDE light curves show a smooth “rapid rise, slow fall” trend. However, the AT2023lli deviates significantly from this pattern.

Optical monitoring showed that there was a strong “bump” in its early light curve, which lasted for nearly a month and was two months away from the main peak. This prolonged and pronounced “collision” is unprecedented in TDE observations. The researchers suggested that the “collision” may be the result of self-intersection of stream fragments, while the main peak may be produced by discharges that are reprocessed during accretion.

Additionally, the researchers observed delayed and intermittent X-ray emission compared to optical/ultraviolet (UV) radiation, which they attributed to the accretion disk being obscured by outflowing material, causing soft X-rays to be absorbed and reprocessed into optical/ultraviolet (UV) radiation. The intermittency in X-ray emission is thought to be due to the presence of an uneven reprocessing layer around the accretion disk, which may be related to an uneven distribution of obscuring material.

This study highlights the importance of high-tempo, multi-wavelength sampling in understanding the physical processes of TDE. During the later development of AT2023lli, the sensitivity of the WFST was highlighted in providing high-quality multicolor photometric data.

The unique survey design of the WFST high-tempo deep field, coupled with the recently launched Einstein detector, brings hope for discoveries in transient source studies, including TDE.