Sgr A*, which is the strong radio emission region at the center of our galaxy, has largely affected by the scattering medium along with our line of sight. The scattering medium causes a angular broadening of the measured size of Sgr A* by refracting the emission. One of our goal is to resolve the very inner region of the supermassive black hole, so measuring the size and structure of Sgr A* is quiet important. Therefore, constraining the properties of scattering medium is one of the main goal for Sgr A* study. Here, two researches suggested the location of the scattering medium by studying an ambient magnetar, J1745-2900. We will see each result and the way of their study.