Formation of Sources for Solar Cosmic Rays in Eruptive Flares X6.9 and M5.1 Observed August 9, 2011, and May 17, 2012

Abstract

A coronal mass ejection (CME) and solar proton event (SPE) succeeding weak flares in soft X-rays and being observed in the interplanetary space (IS) is not any unusual. However, it remains unclear in what way extreme CME and SPE characteristics can be realized in such cases. The present work compares solar and IS observations associated with the long-term M5.1 flare of an ulterior impulsive phase (comparatively weak electromagnetic radiation (EMR)) and short powerful X6.8 flare of a bright impulsive phase (strong EM radiation) observed on May 17, 2012 and August 9, 2011, respectively. Both flares were accompanied by powerful IS fluxes of solar cosmic rays (SCR), which were protons above 100 MeV and electrons above 1 MeV, and by fast coronal mass ejections with velocities exceeding 1500 km/s. Comparing the CME and SCR parameters as well as those of flare EMR on time scales from several minutes to several hours (succeeding the onsets of M5.1 and X6.8 non-thermal radiation), we find that CME and SCR characteristics have been formed by the duration of flare processes but not by their intensity. A longer and more intensive IS escape of solar protons in the M5.1 event compared with X6.8 is attributed to the flare occurring only in the corona, i.e., without any evident "chromospheric evaporation" that is without significant changes in temperatures ${{\left( {dT{/}dt} \right)}_{{{M5}{.1}}}} < {{\left( {dT{/}dt} \right)}_{{{X6}{.8}}}}$ and emission measures ${{\left( {dEM{/}dt} \right)}_{{{M5}{.1}}}} < {{\left( {dEM{/}dt} \right)}_{{{X6}{.8}}}}$, and to the lower CME acceleration ${{a}_{{{M5}{.1}}}} < {{a}_{{{X6}{.8}}}}$ resulting in longer duration ${{t}_{{{M5}{.1}}}} = V_{{{M5}{.1}}}^{{{max}}}{/}{{a}_{{{M5}{.1}}}} > V_{{{X6}{.8}}}^{{{max}}}{/}{{a}_{{{X6}{.8}}}} = {{t}_{{{X6}{.8}}}}$ required for reaching the maximum velocity. Longer CME accelerations imply longer processes of the energy release (acceleration) occurring in the flare decay phase. These processes occurred in the system of high post-flare loops, with their plasma densities and magnetic fields being insufficient for generating hard X-rays and microwave radiation exceeding the detection thresholds of current instruments. Only the long-term γ radiation detected by the FermiLAT instrument and continued CME acceleration indicated the energy release occurring.