Effects of magnetic diffusivity on the tears mode instability in the flares of the SGR A

We investigate the effects of the magnetic diffusivity on the tears mode instability during the process of magnetic reconnection in the accretion flow around Sgr A* via 2D simulation. It is believed that the magnetic diffusivity plays an important role during the magnetic reconnection, so the temperature-dependent diffusivity eta TD is applied in this work. For comparison, the case with constant diffusivity eta C is also studied. In our simulations, there are many plasmoids formed due to the magnetic reconnection, and these plasmoids consequently merge many times. It is found that the temperature-dependent diffusivity will cause more frequent merger of the plasmoids. Because of the turbulence of the current sheet, the temperature distribution is non-uniform, so at the secondary X-points with the different temperature, a lot of plasmoids form and merge to become larger plasmoids. Then the larger plasmoids merge to become a huge plasmoid. In the case of the constant magnetic diffusion, the plasmoid merge less frequently than in the case of the temperature-dependent diffusivity. The huge plasmoid forms and then moves up from the current sheet in both cases. In the case with the temperature-dependent diffusivity, the huge plasmoids oscillate and deform for a long time. This phenomenon is not obvious in the case of the constant diffusivity; in this case the huge plasmoids form and then move out from the upper boundary of the simulation area without oscillation and deformation.