Similar ratios of the rise timescale to the decline timescale of optical light curves in common tidal disruption events

The entirely similar physical process in tidal disruption events (TDEs) basically indicates that just one parameter might distinguish the variability properties of TDEs from that of other transient events that have different physical processes. We report such a parameter, the timescale ratio R_2/1,rd of the rise timescale t_1/2,r (from half maximum to maximum) to the decline timescale t_1/2,d (from maximum to half maximum). We define this based on 34 optical TDEs with reported t_1/2,r and t_1/2,d. Among the 34 optical TDEs, AT2020wey is an outlier with R_ 2/1,rd which is 4.5 times higher than the mean value 0.6 of the other optical TDEs. However, when the similar but more flexible model functions are considered, the redetermined R_2/1,rd is ∼0.9 in AT2020wey. This is very similar to the values of the other optical TDEs. Therefore, the parameter R_ 1/2,rd might be a potential classification parameter for optical TDEs. Furthermore, R_1/2,rd were determined in the unique optical transients AT2019avd, PS1-10adi, SDSS J0946+3512, and J2334+1457. The second flare with R_ 1/2,rd in AT2019avd is expected to be very different from that of other optical TDEs, but PS1-10adi, SDSS J0946+3512, J2334+1457, and the first flare in AT2019avd are expected to be similar to the other optical TDEs. In the near future, the properties of R_1/2,rd determined on a large sample of optical transients might provide further clues to support whether R_1/2,rd might be a better classification parameter to distinguish TDEs from other transient events.