Energy partition in a confined flare with an extreme-ultraviolet late phase

Abstract

Aims. In this paper, we reanalyze the M1.2 confined flare with a large extreme-ultraviolet (EUV) late phase on 2011 September 9, focusing on its energy partition. Methods. The flare was observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The three-dimensional (3D) magnetic fields of active region 11283 before flare were obtained using the nonlinear force free field modeling and the vector magnetograms observed by the Helioseismic and Magnetic Imager (HMI) on board SDO. Properties of the nonthermal electrons injected into the chromosphere were obtained from the hard X-ray observations of the Ramaty Hight Energy Solar Spectroscopic Imager (RHESSI). Soft X-ray fluxes of the flare were recorded by the GOES spacecraft. Irradiance in 1−70 Å and 70−370 Å were measured by the EUV Variability Experiment (EVE) on board SDO. Various energy components of the flare are calculated.Results. The radiation (∼5.4×10 30 erg) in 1−70 Å is nearly eleven times larger than the radiation in 70−370 Å, and is nearly 180 times larger than the radiation in 1−8 Å. The peak thermal energy of the post-flare loops is estimated to be (1.7−1.8)×10 30 erg based on a simplified schematic cartoon. Based on previous results of Enthalpy-Based Thermal Evolution of Loops (EBTEL) simulation, the energy inputs in the main flaring loops and late-phase loops are (1.5−3.8)×10 29 erg and 7.7×10 29 erg, respectively. The nonthermal energy ((1.7−2.2)×10 30 erg) of the flare-accelerated electrons is comparable to the peak thermal energy and is sufficient to provide the energy input of the main flaring loops and late-phase loops. The magnetic free energy (9.1×10 31 erg) before flare is large enough to provide the heating requirement and radiation, indicating that the magnetic free energy is adequate to power the flare.