We report new ( 1995 ) Very Large Array observations and ( 1984–1999 ) Effelsberg 100m monitoring observations of the 22 GHz H _ { 2 } O maser spectrum of the Seyfert 2 galaxy NGC 1068 .
The sensitive VLA observations provide a registration of the 22 GHz continuum emission and the location of the maser spots with an accuracy of \sim 5 mas .
Within the monitoring data , we find evidence that the nuclear masers vary coherently on time-scales of months to years , much more rapidly than the dynamical time-scale .
We argue that the nuclear masers are responding in reverberation to a central power source , presumably the central engine .
Between October and November 1997 , we detected a simultaneous flare of the blue-shifted and red-shifted satellite maser lines .
Reverberation in a rotating disk naturally explains the simultaneous flaring .
There is also evidence that near-infrared emission from dust grains associated with the maser disk also responds to the central engine .
We present a model in which an X-ray flare results in both the loss of maser signal in 1990 and the peak of the near-infrared light-curve in 1994 .
In support of rotating disk geometry for the nuclear masers , we find no evidence for centripetal accelerations of the redshifted nuclear masers ; the limits are \pm 0.006 km s ^ { -1 } year ^ { -1 } , implying that the masers are located within 2° of the kinematic line-of-nodes .
We also searched for high velocity maser emission like that observed in NGC 4258 .
In both VLA and Effelsberg spectra , we detect no high velocity lines between \sim \pm 350 km s ^ { -1 } – \pm 850 km s ^ { -1 } relative to systemic , arguing that masers only lie outside a radius of \sim 0.6 pc ( 1.9 light-years ) from the central engine ( assuming a distance of 14.4 Mpc ) .
We also consider possible models for the jet masers near radio continuum component C. We favor a shock-precursor model , in which the molecular gas surrounding the jet is heated by X-ray emission from a shock front between the jet and a molecular cloud .