Number of positrons injected at the outburst in the CMZ, which makes it possible to reproduce a 511 keV flux of 5 × 10^-4 ph cm^-2 s^-1 outside the CMZ (R> 200 pc) today, as a function of time since outburst. The curves are shown only over the time intervals when the flux inside the CMZ (R< 200 pc) is below the observed 1.5 × 10^-4 ph cm^-2 s^-1 (hence the truncations of the left parts). The solid red, dotted black, and dashed blue curves correspond to the simulations carried out with a X-shaped, dipole, and no halo GMF configurations.