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

Abstract

Totally similar physical process in tidal disruption events (TDEs) basically indicates that there should be potential parameter to distinguish variability properties of TDEs from the other transient events having different physical processes. Here, we try to report such a parameter, the timescale ratio $R_{2/1,rd}$ of rise timescale $t_{1/2,r}$ (from half-max to maximum) to decline timescale $t_{1/2,d}$ (from maximum to half-max), especially based on the 34 optical TDEs with reported $t_{1/2,r}$ and $t_{1/2,d}$. Among the 34 optical TDEs, AT2020wey is an outlier with $R_{2/1,rd}\sim2.7$ which is 4.5 times larger than the mean value 0.6 of the other optical TDEs. However, after considering similar but more flexible model functions, the re-determined $R_{2/1,rd}$ is $\sim$0.9 in AT2020wey, totally similar as the values of the other optical TDEs. Therefore, the parameter $R_{1/2,rd}\sim0.6$ could be a potential classification parameter for optical TDEs. Furthermore, $R_{1/2,rd}$ have been checked in the unique optical transients of AT2019avd, PS1-10adi, SDSS J0946+3512 and J2334+1457. We can find that the second flare with $R_{1/2,rd}\sim11$ in AT2019avd should be very different from the other optical TDEs, but PS1-10adi, SDSS J0946+3512, J2334+1457 and the first flare in AT2019avd should be similar as the other optical TDEs. In the near future, properties of $R_{1/2,rd}$ through large sample of optical transients could provide further clues to support whether $R_{1/2,rd}$ could be a better classification parameter to distinguish TDEs and the other transient events.

Figures (8)

• Figure 1: Properties of $R_{1/2,rd}$. X-labels from 1 to 34 mark the Rank No. of the 33 optical TDEs in yr23 and AT2024tvd in yr25. Solid red circle plus error bars mark the results for AT2020wey. Solid red five-point-star plus error bars mark the modified results in AT2020wey. Solid circle in dark green (Rank No.=35) shows the results for the first flare in AT2019avd, and the up arrow in purple (Rank No.=36) shows the $R_{1/2,rd}\sim11$ higher than the current marked position for the second flare in AT2019avd. Open circle (Rank No.=37), solid triangle (Rank No.=38) and open triangle (Rank No.=39) plus error bars in dark green show the results in PS1-10adi, SDSS J0946+3512 and J2334+1457. Open circles plus error bars in red show the re-measured $R_{1/2,rd}$ of the 32 TDEs (except AT2020wey) in yr23. Horizontal solid and dashed line in blue and in red mark the mean value and $\pm$ standard deviation of the $R_{1/2,rd}$ in yr23 and the re-measured $R_{1/2,rd}$ through ZFPS r-band background-subtracted light curves in this manuscript.
• Figure 2: Results for AT2020wey. Left panel shows the ZTF gr-band light curves (symbols in blue and in red) of AT2020wey in rest frame, with horizontal dashed lines marking the determined apparent magnitudes of the host galaxy contributions. Middle panel shows the $LC_{g,TDE}(t)$ (blue symbols) and $LC_{r,TDE}(t)$ (red symbols) after subtractions of the host galaxy contributions. In middle panel, solid and dashed lines in blue and in red show the mathematical method determined best descriptions and corresponding 1RMS scatters to the $LC_{g,TDE}(t)$ and $LC_{r,TDE}(t)$, respectively. The corresponding parameters are marked in blue and red characters. Vertical solid lines in blue and in red mark the peak positions of the best fitting results to the $LC_{g,TDE}(t)$ and $LC_{r,TDE}(t)$, the vertical dotted lines in blue and in red mark the corresponding positions for the half-max of the best fitting results. Right panel shows the new descriptions to the $LC_{g,TDE}(t)$ and $LC_{r,TDE}(t)$ by the modified formula, with symbols and line styles having the same meanings as those in the middle panel.
• Figure 3: Results for AT2019avd. Left panel shows the ZTF g-band light curve in rest frame, with horizontal dashed red line marking the determined apparent magnitude of the host galaxy contributions. Middle panel shows the $LC_{g,TDE}(t)$ of the first flare, after subtractions of the host galaxy contributions. In middle panel, solid and dashed lines in red show the mathematical method determined best descriptions and corresponding 1RMS scatters. The corresponding parameters are marked in blue characters. Vertical solid and dotted lines in blue mark the peak and half-maximum positions of the best fitting results. Right panel shows the results for the second flare, with symbols and line styles having the same meanings as those in the middle panel.
• Figure 4: Results for the transients of PS1-10adi (left), SDSS J0946+3512 (middle) and J2334+1457 (right). Top right corner of each panel shows the light curve in rest frame, with horizontal dashed red line marking the determined apparent magnitude of host galaxy contributions. In main body of each panel, solid and dashed lines in red show the best descriptions and corresponding 1RMS scatters to the $LC_{TDE}(t)$, after subtractions of the host galaxy contributions, with symbols and line styles have the same meanings as those in the right panel of Fig. \ref{['cd22']}.
• Figure 5: Results on background-subtracted ZFPS light curves of AT2020wey in rest frame. Top panel shows the ZFPS gr-band background-subtracted light curves (symbols in blue and in red) in flux space, including the data points with measurements smaller than 3 times of their uncertainties. Horizontal dashed red line marks flux equal to zero. Middle panel and bottom panel show the best fitting results to the background-subtracted light curves with measurements larger than 3 times of their uncertainties around the TDE related flare with MJD-58000 between 1100 and 1200, with symbols and line styles having the same meanings as those in the middle panel and right panel in Fig. \ref{['lmc']}.