  The origin of relativistic solar protons during large flare/CME events has
not been uniquely identified so far.We perform a detailed comparative analysis
of the time profiles of relativistic protons detected by the worldwide network
of neutron monitors at Earth with electromagnetic signatures of particle
acceleration in the solar corona during the large particle event of 20 January
2005. The intensity-time profile of the relativistic protons derived from the
neutron monitor data indicates two successive peaks. We show that microwave,
hard X-ray and gamma-ray emissions display several episodes of particle
acceleration within the impulsive flare phase. The first relativistic protons
detected at Earth are accelerated together with relativistic electrons and with
protons that produce pion decay gamma-rays during the second episode. The
second peak in the relativistic proton profile at Earth is accompanied by new
signatures of particle acceleration in the corona within approximatively 1
solar radius above the photosphere, revealed by hard X-ray and microwave
emissions of low intensity, and by the renewed radio emission of electron beams
and of a coronal shock wave. We discuss the observations in terms of different
scenarios of particle acceleration in the corona.
