Speaker
Description
We report on the sources of gamma-ray emission above 100 MeV in the very impulsive GOES M3.3 class flare SOL2012-06-03. The >100 MeV emission during the prompt phase displayed a double-peaked temporal structure, with the highest peak occurring 17$\pm$2 seconds after the first peak with a difference in flux of almost a factor of 3. The HXR and gamma-ray time profiles during the impulsive phase seem to indicate two separate acceleration mechanisms at work. The first appears to be flare-related, with the HXR and gamma-ray peaks coinciding in time and shape, whereas the second gamma-ray peak has no visible HXR or radio counterpart. This behavior suggests a potentially pure ion acceleration mechanism. AIA imaging shows a bright elliptical ribbon and a transient brightening in a region on the north-western (NW) side of the ribbon. An erupting flux rope, visible in all the AIA EUV filters seconds prior to the start of the second gamma-ray peak, is found to propagate towards the NW direction and a coronal wave is also observed in association with this event. This global wave also has fastest expansion towards the NW. The time profile of the 94 and 335 A intensity of the NW region shows that the fastest increase coincides with the time that the second gamma-ray peak reaches its maximum value, indicating a coupling between the two. Nonlinear force-free extrapolations at the time of the impulsive peaks show closed loops connecting the NW region to the south-eastern part of the elliptical flare ribbon and the magnetic topology of the region revealed clusters of nulls running along the western edge of the flaring region towards the NW transient brightening. These observations suggest a spine-and-fan geometry, and based on these observations we interpret the second gamma-ray peak as being due to null-point reconnection accelerating predominately ions to relativistic energies. The >100 MeV emission from this flare also exhibits a delayed phase with an exponential decay of roughly 350 seconds. We find that the delayed emission is consistent with ions being trapped in a closed flux tube with gradual escape via their loss cone to the chromosphere.
| Collaboration(s) | Fermi-LAT |
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