VLBI observations of SgrA* at burst time in 2001

M.Miyoshi1,H.Imai2, J.Nakashima3, S.Deguchi3 and Z.Shen4

1 National Astronomical Observatory Japan, 2-21-1, Osawa Mitaka Tpkyo, 181-8588
2 Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, the Netherlands
3 Nobeyama Radio Observatory, Minamimaki Minamisaku Nagano Japan, 384-1305
4 The Institute of Space and Astronautical Science, 3-1-1 Yunodai Sagamihara Kanagawa Japan 229-8510

E-mail contact: miyoshi@miz.nao.ac.jp

SgrA* is one of the most promising sources that in future we can observe the vicinity of massive black holes with sub millimeter VLBI (Falcke et al. 2000). Previous VLBI observations at millimeter waves report that intervening thermal plasma deforms the true SgrA* figure to an elliptical Gaussian shape.

We have performed three epochs VLBA observations of SgrA* centered@at burst time in 2001 July and detected some fringes from longer baselines connecting to SC station at 43GHz. From the results, we would check again the possibility whether millimeter VLBI can reveal the true figure of SgrA* or not.

Our observations originally aimed at detecting proper motions of SiO maser sources (=late type stars) located within a few light years from SgrA*. We also show preliminary results of the proper motion study and estimation of enclosed mass of about 2.5 x 10^6 M_sun within light year radius. This means most of mass are still concentrated at central massive black hole in light year region of Galactic Center.