Fine magnetic characteristics of a light bridge observed by Hinode

Light bridge (LB) is bright structure crossing the umbra of sunspots and associated to the breakup or assembly of sunspots. In this paper, a LB is presented and studied using the observatory data obtained by Hinode satellites. Force-free factor (α) and the z-component of current (Jz) and tension force (Tz) are calculated basing on the vector magnetograms observed by Spectro-Polarimeter (SP) of the Solar Optical Telescope (SOT) on board Hinode. It is found that the amplitudes of α and Jz of LB are generally larger than those of umbra. It is found that there are two signs of Jz along LB, which are divided at near the middle position of LB. It is found that the amplitudes of Tz of LB are smaller than those of umbra and there are changes of sign of Tz between the boundary of LB and umbra. Through comparisons and investigations, it suggest that LB and umbra maybe two different magnetic systems, which is a necessary condition for interaction magnetic reconnection.