Multiwavelength diagnostics of the precursor and main phases of an M1.8 flare on 2011 April 22

Abstract

We study the temporal, spatial and spectral evolution of the M1.8 flare,\nwhich occurred in NOAA AR 11195 (S17E31) on 22 April 2011, and explore the\nunderlying physical processes during the precursors and their relation to the\nmain phase. The study of the source morphology using the composite images in\n131 {\\deg}A wavelength observed by the SDO/AIA and 6-14 keV revealed a\nmultiloop system that destabilized systematically during the precursor and main\nphases. In contrast, HXR emission (20-50 keV) was absent during the precursor\nphase, appearing only from the onset of the impulsive phase in the form of\nfoot-points of emitting loop/s. This study has also revealed the heated\nloop-top prior to the loop emission, although no accompanying foot-point\nsources were observed during the precursor phase. We estimate the flare plasma\nparameters viz. T, EM, power-law index, and photon turn-over energy by forward\nfitting RHESSI spectral observations. The energy released in the precursor\nphase was thermal and constituted ~1 per cent of the total energy released\nduring the flare. The study of morphological evolution of the filament in\nconjunction with synthesized T and EM maps has been carried out which reveals\n(a) Partial filament eruption prior to the onset of the precursor emission, (b)\nHeated dense plasma over the polarity inversion line and in the vicinity of the\nslowly rising filament during the precursor phase. Based on the implications\nfrom multi-wavelength observations, we propose a scheme to unify the energy\nrelease during the precursor and main phase emissions in which, the precursor\nphase emission has been originated via conduction front formed due to the\npartial filament eruption. Next, the heated leftover S-shaped filament has\nundergone slow rise and heating due to magnetic reconnection and finally\nerupted to produce emission during the impulsive and gradual phases.\n