On some large solar energetic particle events: Direct impulsive component and broad associated coronal mass ejections

Using the proton intensity and X-ray flux data from the GOES, combined with the observations of the associated solar eruptions by the Large Angle and Spectrometric Coronagraph Experiment (LASCO) on board the Solar and Heliospheric Observatory (SOHO), 14 large SEP events occurring in the period 2000 January–2002 April have been studied. It is found that: (1) events with the SEPs increasing shortly after the maximum of their parent flares (<1 h; hereafter prompt events) have rapid and great (up to four orders of magnitude) SEP increments in high-energy channels (> ～100 MeV); however, for events whose onset of the SEP injection lags the flare maximum for a long time (>3 h; hereafter delayed events), the high-energy SEPs show no obvious enhancements (within one order of magnitude); (2) peak intensity of the prompt events is distinctly larger than that of the delayed events; (3) CMEs associated with the poorly magnetically connected events (source region <W30°) in our survey are all halo CMEs. From these observational differences, we propose a special scenario of the production of the largest SEP events: both CMEs and flares are induced in the same coronal process; high-energy particles accelerated in the reconnection region can escape easily from the open field lines and/or be transported by fast CMEs into interplanetary space, indicating a direct impulsive component in large gradual SEP events. Meanwhile, the broad width of the associated CMEs implies that the CME width is more important in SEP events production than previously considered.