DG Tau A , a class-II young stellar object ( YSO ) displays both thermal , and non-thermal , radio emission associated with its bipolar jet .
To investigate the nature of this emission , we present sensitive ( \upsigma \sim 2 { ~ { } \upmu Jy } \mathrm { beam } ^ { -1 } ) , Karl G. Jansky Very Large Array ( VLA ) 6 and 10 { ~ { } GHz } observations .
Over 3.81 { ~ { } yr } , no proper motion is observed towards the non-thermal radio knot C , previously thought to be a bowshock .
Its quasi-static nature , spatially-resolved variability and offset from the central jet axis supports a scenario whereby it is instead a stationary shock driven into the surrounding medium by the jet .
Towards the internal working surface , knot A , we derive an inclination-corrected , absolute velocity of 258 \pm 23 \hbox { $ { ~ { } { ~ { } km } { ~ { } s } ^ { -1 } } $ } .
DG Tau A ’ s receding counterjet displays a spatially-resolved increase in flux density , indicating a variable mass loss event , the first time such an event has been observed in the counterjet .
For this ejection , we measure an ionised mass loss rate of ( 3.7 \pm 1.0 ) \times 10 ^ { -8 } \hbox { $ { ~ { } M _ { \odot } } $ } { ~ { } yr } ^ { -1 } during the event .
A contemporaneous ejection in the approaching jet isn ’ t seen , showing it to be an asymmetric process .
Finally , using radiative transfer modelling , we find that the extent of the radio emission can only be explained with the presence of shocks , and therefore reionisation , in the flow .
Our modelling highlights the need to consider the relative angular size of optically thick , and thin , radio emission from a jet , to the synthesised beam , when deriving its physical conditions from its spectral index .