NGC 4261 ( 3C 270 ) is an elliptical galaxy containing a 300-parsec scale nuclear disk of gas and dust imaged by the Hubble Space Telescope ( HST ) , around a central supermassive black hole .
Previous VLBI observations of NGC 4261 revealed a gap in emission in the radio counterjet , presumably due to free-free absorption in the inner parsec of the accretion disk .
Here we present three 8 GHz VLBA observations of NGC 4261 that allow us to monitor the location and depth of the gap , and check for motions in the jet and counterjet .

The separation between the brightest peak and the gap is stable , with an upper limit to its motion of 0.01 c , supporting the interpretation of the gap as absorption by an accretion disk rather than an intrinsic jet feature .
These observations span a time of order that required for orbiting material in the disk to transit the counterjet , so we are able to search for density changes ( clumps ) in the disk by monitoring the optical depth of the gap .
The optical depth of the gap is stable to within 20 % over 5 years at \tau = 1.1 \pm 0.1 , corresponding to an electron density in the disk that is constant to within 10 % .

We measure an apparent speed in the jet of 0.52 \pm 0.07 c .
An apparent speed could not be measured for the counterjet due to a lack of identifiable features .
From the apparent jet speed and the jet to counterjet brightness ratio , we calculate the viewing angle of the jet to be 63 \pm 3 \hbox { $ { } ^ { \circ } $ } and its intrinsic speed to be 0.46 \pm 0.02 c .
From the inclination and position angles of the parsec-scale radio jet and outer HST disk rotation axis we calculate a difference between the parsec-scale radio jet and outer HST disk rotation axis of 12 \pm 2 \hbox { $ { } ^ { \circ } $ } .
Because of its well-defined HST disk and bright parsec-scale radio jet and counterjet , NGC 4261 is ideal for studying the combined disk-jet system , and this is the first case known to us where both the inclination and position angles of both the disk and jet have been determined .