H2O and OH masers as probes of the obscuring torus in NGC 1068

We report the discovery of OH masers and positionally resolved H2O maser emission in the nucleus of NGC 1068. The brightest H2O masers are associated with the radio continuum component that is probably the location of the central engine (Gallimore, Muxlow, and coworkers). These masers trace a similar to 50 mas (similar to 5 pc), roughly linear velocity gradient along P.A. 94 degrees +/- 4 degrees, which is almost at right angles to the local radio jet axis. The kinematics of the masers are well described as an edge-on Keplerian disk surrounding a large central mass concentration (black hole?). The inner radius of the maser disk is greater than or similar to 1.3 pc, and the outer radius is similar to 2.5 pc, assuming a distance of 22 Mpc. The mass within the inner radius, normalized to the best-fit disk parameters, is 4.4 x 10(7) M. x (r(in)/1.3 pc) (v(max)/378 km s(-1))(2). These masers might occur in the parsec-scale torus thought to obscure the central engine. Radio continuum emission fills the region interior to the H2O masers, in agreement with the prediction that the continuum emission is thermal free-free radiation from the inner face of the molecular torus (Gallimore and coworkers). The location of the OH masers and nuclear H I absorption (Gallimore and coworkers), measured with similar to 1 '' angular resolution, is consistent with the location of the H2O masers associated with the central engine. The H I absorption profile is also consistent with the Keplerian model for the H2O maser disk kinematics, and the velocity range of the OH masers is similar to that spanned by both the H I and H2O spectral features. It therefore seems likely that the OH masers and H I absorption also originate in the obscuring material surrounding the central engine. The OH masers indicate the presence of a more tenuous molecular medium in the torus, in addition to the denser material traced by the H2O maser emission. We have also discovered fainter H2O masers located 0.'' 3 (similar to 30 pc) downstream along the radio jet. These masers are too distant from the central engine to arise in a parsec-scale torus. They may instead occur at the shock interface between the radio jet and an intervening molecular cloud. The implication is that H2O magamaser emission may probe both circumnuclear disks and shock fronts in other active galactic nuclei.