Two Epochs of Very Large Array Observations of Water Maser Emission in
  the active galaxy NGC 6240
  Studies of 22GHz H2O maser emission from the merging galaxy NGC 6240 with
double nuclei are presented. Two epochs of Very Large Array (VLA) observations
in the A-configuration in spectral-line mode were carried out at 0.1 arcsec
resolution by covering the redshifted velocity range of ~ 300 km/s with respect
to the systemic velocity of the galaxy. The purpose of these new observations
is twofold: to detect an H2O maser that an earlier VLA observation pinpointed
in the southern nucleus in the northern nucleus as well to clarify the
kinematics of the double nuclei, and to understand the origin of the maser in
the galaxy. In the second epoch, one velocity feature peaking at Vlsr=7491.1
km/s, redshifted by ~200 km/s relative to the systemic velocity, was detected
only toward the southern nucleus. The detection of an H2O maser feature at or
near this velocity had never been reported in earlier observations. However,
including the known velocity features at redshifted velocities, no other
velocity features were observed toward either nuclei throughout these epochs.
The maser remains unresolved at an angular resolution of ~ 0".1, corresponding
to a linear size of less than about 45 pc. The two epochs of VLA observations
show that the maser intensity is variable on timescales of at least three
months, while the correlation between the maser intensity and the radio
continuum intensity is not certain from our data. It is plausible that the
maser in NGC 6240 is associated with the activity of an active galactic nucleus
in the southern nucleus. Alternatively, the maser can be explained by
starforming activity at the site of massive starformation in the galaxy.
