Extreme Solar Flares on the Archival Data about Proton Events

One of serious challenges to the problem of radiation hazard in space is a lack of a clear, unambiguous relation between the fluxes (fluences) of relativistic SCR and non-relativistic SEPs. Modern concept of Extreme Solar Event (ESE) is critically analyzed based on available direct/proxy data on solar cosmic rays (SCR), or solar energetic particles (SEPs). Special attention is paid to recent debate on the validity, origin and properties of the events AD1859 (Carrington event) identified by nitrate method and AD775, AD994 and 3372 BC by radionuclide data. In spite of existing uncertainties in proton fluences above 30 MeV, all of them are fitted well by a unique distribution function, at least, with present level of solar activity. Extremely large SEP fluxes (fluences) are shown to obey a probabilistic distribution with a sharp break in the range of large fluences (or low probabilities). The studies of this kind may be extended for the periods with different levels of solar activity in the past and/or in the future. Considering the confirmation of super-flares on Sun-like stars, this issue merits attention.