We present new Karl G. Jansky Very Large Array observations of the compact ( \sim 0 \mbox { $ { } ^ { \prime \prime } \hskip { -7.6 pt } . $ } 05 ) , time-variable radio source projected near the center of the ultracompact HII region W3 ( OH ) .
The analysis of our new data as well as of VLA archival observations confirms the variability of the source on timescales of years and for a given epoch indicates a spectral index of \alpha = 1.3 \pm 0.3 ( S _ { \nu } \propto \nu ^ { \alpha } ) .
This spectral index and the brightness temperature of the source ( \sim 6,500 K ) suggest that we are most probably detecting partially optically thick free-free radiation .
The radio source is probably associated with the ionizing star of W3 ( OH ) , but an interpretation in terms of an ionized stellar wind fails because the detected flux densities are orders of magnitude larger than expected .
We discuss several scenarios and tentatively propose that the radio emission could arise in a static ionized atmosphere around a fossil photoevaporated disk .