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

Abstract

ABSTRACT 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 ηTD is applied in this work. For comparison, the case with constant diffusivity ηC 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.