Magnetic helicity injection in NOAA 11261 associated with flares

Xu Haiqing, xhq@bao.ac.cn, National Astronomical Observatories, Chinese Academy of Sciences, China
Zhang Hongqi, hzhang@bao.ac.cn, National Astronomical Observatories, Chinese Academy of Sciences
Su Jiangtao, sjt@bao.ac.cn, National Astronomical Observatories, Chinese Academy of Sciences
Ruan Guiping, Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics,Shandong University at Weihai
Liu Jihong, Department of physics electrical engineering department of information, Shi Jiazhuang University

Abstract
We investigated the variation of magnetic helicity injection through the photospheric surface of the flare-productive active region NOAA 11261 during 7 days. The helicity injection was determined using line-of-sight magnetograms with 720-second cadence taken by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We found that a mount of positive helicity was injected before the first M9.3 flare erupted, and then negative helicity was injected during the last four M class flares. The density of helicity injection rate is relatively large where the flares erupted which may trigger the flare. The shear is very strong near the magnetic neutral line and four flares erupted.