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

¹ Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, CAS, Nanjing 210023, PR China
e-mail: zhangqm@pmo.ac.cn
² Key Laboratory of Planetary Sciences, Shanghai Astronomical Observatory, Shanghai 200030, PR China
³ CAS Key Laboratory of Solar Activity, National Astronomical Observatories, CAS, Beijing 100101, PR China
⁴ School of Astronomy and Space Science, Nanjing University, Nanjing 210023, PR China
⁵ State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, PR China

Received: 3 April 2020
Accepted: 8 April 2021

Abstract

Aims. In this paper, we reanalyze the M1.2 confined flare with a large extreme-ultraviolet (EUV) late phase on 2011 September 9, with a focus 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 the active region 11283 prior to the flare were obtained using nonlinear force free field modeling and the vector magnetograms observed by the Helioseismic and Magnetic Imager (HMI) on board the 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 the SDO. We calculated various energy components of the flare.

Results. The radiation (∼5.4 × 10³⁰ 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) × 10³⁰ erg based on a simplified schematic cartoon. Based on previous results of the 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) × 10²⁹ erg and 7.7 × 10²⁹ erg, respectively. The nonthermal energy ((1.7−2.2) × 10³⁰ 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 × 10³¹ erg) before flare is large enough to provide the heating requirement and radiation, indicating that the magnetic free energy is sufficient to power the flare.