Quasi-periodic pulsations in solar and stellar flares. Review

This paper provides an overview of the state-of-the-art studies of oscillatory processes in solar and stellar flares, based on modern observational data from ground-based and space-borne instruments with high temporal, spatial, and spectral resolution in different electro-magnetic spectrum ranges. We examine the mechanisms that generate flare emission and its quasi-periodic modulation. We discuss similarities and differences between solar and stellar flares, and address associated problems of superflares on the Sun and space weather problems. Quasi-periodic pulsations (QPPs) of flare radiation are shown to be an effective tool for diagnosing both the flare processes themselves and the parameters of flare plasma and accelerated particles. We consider types of QPPs, their statistical properties, and methods of analysis, taking into account the non-stationarity of the QPPs’ parameters. We review the proposed mechanisms of QPPs and address open questions.