2022PASP..134d4101L

We have systemically studied the properties of 1ES 1959+650, specifically its multiband variability and emission mechanisms. We carefully analyze multiband variability properties by four different kinds of trusted approaches. In contrast with previous research and thanks to our more detailed data, we find that an unprecedented significant quasi-periodic component with timescale P=266.2_–7.2^+7.5 in the optical R band indeed exists. We suggest that this light curve may result from accretion flow instabilities. Further, among the multiband spectra, we find no significant correlation between different bands, which implies that the physical origin of the dominant radiation for different bands is not the same. Motivated by these results, we go on further to study the radiation mechanisms based on quasi-simultaneous spectra. Here, a model that self-consistently involves protons, electrons, and photons is used to study the light curve and interpret the spectral energy distribution of 1ES 1959+650. Considering the variability properties and model calculation, we suggest that the variation of the cutoff energy of electrons and protons may dominate the variability of X-ray and γ-ray bands in 1ES 1959+650.