Lomb-Scargle periodograms of AT2019aalc from ZTF forced photometry, binned to 1-day intervals. Panel (a): Periodograms for the first flare of AT2019aalc, using data from the time of its peak up to the onset of the next flare (58700 − 59900 MJD). To account for the underlying fading of the continuum beyond the first flare, we subtracted a fourth-degree polynomial fit. Panel (b): Periodograms of the second flare of AT2019aalc (60200 − 60730 MJD). In this case, a second-degree polynomial was subtracted to remove the continuum. Uncertainties of the period (T) correspond to the FWHM of the detected peaks. The horizontal dotted lines represent the 3σ false-alarm probability thresholds, estimated via bootstrapping. Note that none of the peaks in the i-band light curve of the first flare exceeded 3σ and were thus excluded.