We present the results of single-dish and VLBI observations for the water-vapor masers at the nucleus of the Seyfert 2 , IC 2560 .
We monitored velocities of the maser features with the 45-m telescope of the Nobeyama Radio Observatory .
Using the data of 1995–2006 , the velocity drift rate was detected to be \bar { a } = +2.57 \pm 0.04 km s ^ { -1 } yr ^ { -1 } on the average for 6 systemic features .
The Very Long Baseline Array ( VLBA ) with the Very Large Array ( VLA ) firstly detected a red-shifted and a blue-shifted maser features of IC 2560 , in addition to systemic maser features and a continuum component .
We propose a maser disk in the nuclear region .
The systemic and red-shifted features are emitted from a nearly edge-on disk with the position angle of { \it PA } = -46 ^ { \circ } , which is almost perpendicular to the galactic disk .
Assuming the Keplerian rotation , the radii of the maser disk are r = 0.087 –0.335 pc , and the thickness is 2 H \leq 0.025 pc .
The binding mass is 3.5 \times 10 ^ { 6 } \MO at a distance of D = 26 Mpc , and the mean volume density within the inner radius is 1.3 \times 10 ^ { 9 } \MO pc ^ { -3 } , strongly suggesting a massive black hole at the center .
A continuum component was detected at the 0.2 pc southwest of the disk center , and considered as a jet ejected from the nucleus , with an angle of 70 ^ { \circ } from the disk .
The blue-shifted maser feature is located on the continuum component , being interpreted to be a “ jet maser ” .
The distance to IC 2560 is estimated to be D = 31 ^ { +12 } _ { -14 } Mpc from the geometry of the maser disk and the velocity drift rate .