The left panels show the phase-folded ZTF g, r, and i light curves in green, red, and purple in AB magnitudes. The right panels show one or multiple spectra (normalised). SEDM spectra are shown in grey, and other spectra are shown in black. We indicate the cyclotron harmonics with ‘C_n’. The ‘S’ in the left panel indicates at what phase the spectra were obtained. The light curve of ZTF J0116+4417 is not strictly periodic, as shown in detail in Figure 3.