Investigating the temporal domain of massive ionized jets - I. A pilot study

We present sensitive ($\sigma<10{\rm \mu Jy \, beam^{-1}}$), radio continuum observations using the Australian telescope compact array (ATCA) at frequencies of $6$ and $9$ GHz towards 4 MYSOs. From a previous, less sensitive work, these objects are known to harbour ionized jets associated with radio lobes, which result from shock processes. In comparison with that work, further emission components are detected towards each MYSO. These include extended, direct, thermal emission from the ionized jet's stream, new radio lobes indicative of shocks close ($<10^5\, {\rm au}$) to the MYSO, 3 radio Herbig-Haro objects separated by up to $3.8 {\rm pc}$ from the jet's launching site and an IR-dark source coincident with CH$_3$OH maser emission. No significant, integrated flux variability is detected towards any jets or shocked lobes, and only one proper motion is observed ($1806\pm596\,{\rm km \, s^{-1}}$ parallel to the jet axis of G310.1420+00.7583A). Evidence for precession is detected in all four MYSOs with precession-periods and angles ranging from $66-15480 \, {\rm yr}$ and $6-36 ^\circ$ respectively. Should precession be the result of the influence from a binary companion, we infer orbital radii of $30-1800\, {\rm au} $.