H_2O maser and a plasma obscuring torus in the radio galaxy NGC 1052
  We present multi-frequency simultaneous VLBA observations at 15, 22 and 43
GHz towards the nucleus of the nearby radio galaxy NGC 1052. These three
continuum images reveal a double-sided jet structure, whose relative intensity
ratios imply that the jet axis is oriented close to the sky plane. The steeply
rising spectra at 15-43 GHz at the inner edges of the jets strongly suggest
that synchrotron emission is absorbed by foreground thermal plasma. We detected
H_2O maser emission in the velocity range of 1550-1850 km/s, which is
redshifted by 50-350 km/s with respect to the systemic velocity of NGC 1052.
The redshifted maser gas appears projected against both sides of the jet,
similar to the HI seen in absorption. The H_2O maser gas is located where the
free-free absorption opacity is large. This probably implies that the masers in
NGC 1052 are associated with a circumnuclear torus or disk as in the nucleus of
NGC 4258. Such circumnuclear structure can be the sense of accreting onto the
central engine.
