Water-vapor maser disk at the nucleus of the Seyfert 2 IC 2560

We observed the H₂O maser at the nucleus of the Seyfert 2, IC 2560, using the VLBA and the phased VLA. The systemic, red-shifted and blue-shifted maser features and a continuum component have been detected. 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 PA = −47°. The thickness is 2H < 0.025 pc. The binding mass is 3.5 × 10⁶M_⊙. Assuming the Keplerian rotation, the radii at the disk are r = 0.087-0.335 pc and the rotation velocities are 213-418 km s⁻¹. The mean density within the inner radius is 1.3 × 10⁹M_⊙ pc⁻³, suggesting a massive black hole at the center. A continuum component is considered as a jet ejected from the nucleus, with an angle of 70° from the disk. The blue-shifted maser feature is located on the continuum component, being interpreted to be a `jet maser'.