VLBI Observations of NGC6240: resolving the double nuclei and radio
  supernovae
  The European VLBI Network (EVN) has been used at two epochs in 2003 and 2009
to obtain multi-frequency high-resolution images of the merger galaxy NGC6240
in order to study the radio properties of all compact high-brightness
components in the galaxy. Our observations at milli-arcsecond resolution
detected the northern and southern nuclei and two radio components, which we
interpret as long-lived luminous supernovae associated with the circum-nuclear
starburst activity at the southern nucleus. The new VLBI data support the
presence of an active galactic nucleus (AGN) together with starburst activity
at the southern nucleus and provides some evidence for an AGN at the northern
nucleus. The two nuclei both display an inverted spectrum at lower GHz
frequencies. The spectrum of the southern nucleus indicates thermal free-free
absorption on parsec scales, consistent with the presence of an AGN.
