Two Types of Magnetic Reconnection in Coronal Bright Points and the Corresponding Magnetic Configuration

Zhang Qingmin, zhangqm@nju.edu.cn, School of Astronomy and Space Science, Nanjing University
Chen Pengfei, chenpf@nju.edu.cn, School of Astronomy and Space Science, Nanjing University
Guo Yang, guoyang@nju.edu.cn, School of Astronomy and Space Science, Nanjing University
Fang Cheng, fcheng@nju.edu.cn, School of Astronomy and Space Science, Nanjing University
Ding Mingde, dmd@nju.edu.cn, School of Astronomy and Space Science, Nanjing University

Abstract
Coronal bright points (CBPs) are long-lived small-scale brightenings in the lower corona. They are generally explained by magnetic reconnection. However, the corresponding magnetic configuration and how the reconnection proceeds are not well understood. We carry out a detailed multi-wavelength analysis of two neighboring CBPs on 2007 March 16, one is bigger than the other, as revealed by the X-ray Telescope (XRT) aboard the \emph{Hinode} satellite and the Extreme Ultraviolet Imager (EUVI) aboard the \emph{Solar TErrestrial RElations Observatory}. It is seen that the soft X-ray (SXR) light curves present quasi-periodic flashes with an interval of $\sim$1 hr superposed over the long-lived mild brightenings, suggesting that the SXR brightenings of this type of CBPs might consist of two components: one is the gentle brightenings, and the other is the CBP flashes. It is found that the strong flashes of the bigger CBP are always accompanied by SXR jets. The potential field extrapolation based on photospheric magnetograms indicates that both CBPs are covered by a dome-like separatrix surface, with a magnetic null point above. We propose that the repetitive CBP flashes, as well as the recurrent SXR jets, result from the impulsive null-point reconnection, while the long-lived brightenings are due to the interchange reconnection along the separatrix surface. Although the EUV images at high-temperature lines (e.g., 284 {\AA}) resemble the SXR appearance, the 171 {\AA} and 195 {\AA} channels reveal that the blurry CBP in SXR consists of a cusp-shaped loop and several separate bright patches, which are explained to be due to the null-point reconnection and the separatrix reconnection, respectively.