In the solar corona , magnetic reconnection usually takes place at the singular configuration of magnetic field , in particular near a magnetic null owing to its high susceptibility to perturbations .
In this Letter , we report a rare X-shaped structure , encompassing a magnetic null , above a trans-equatorial quadrupole active region group that is well observed by the Atmospheric Imaging Assembly ( AIA ) .
The observations show that this X-shaped structure is visible in all AIA EUV passbands and stably exists for days .
However , possibly induced by flare activities at the northern part of the quadrupole active region group , the X-shaped structure starts to destabilize and meanwhile a jet erupted near its center at \sim 15:05 UT on 2013 October 7 .
Through the non-linear force-free field modeling , we identify a magnetic null , which is above the quadrupole polarities and well corresponds to the X-shaped structure .
After the jet eruption , the temperature and emission measure of the plasma near the X-shaped structure rise from \sim 2.3 MK and \sim 1.2 \times 10 ^ { 27 } \mathrm { cm } ^ { -5 } at 15:01 UT to \sim 5.4 MK and \sim 3.7 \times 10 ^ { 27 } \mathrm { cm } ^ { -5 } at 15:36 UT , respectively , revealed by the differential emission measure analysis , indicating that magnetic reconnection most likely takes place there to heat the plasma .
Moreover , the height of the null has an increase of \sim 10 Mm , which is most likely due to the partial opening of the field lines near the fan surface that makes the null underneath rise to seek for a new equilibrium .