Proton spectrum of the 2005 January 20 solar flare

An extreme solar cosmic ray event broke out on 2005 January 20.Not only is it the most intensive solar energetic particle (SEP) event,with＞100 MeV particles measured by GOES satellite since 1986,but it has been the largest ground level enhancement (GLE) event recorded by the ground-based neutron monitors since 1956.This work presents the solar proton spectra for this event with data obtained by GOES in multiple energy cbannels.These spectra are well fitted by a modified power-law function.The spectral index of around -1 indicates that the January 20 event has a hard energy spectrum.Possible mechanisms for the acceleration of relativistic protons are discussed.