Variability of the NGC 1333 IRAS 4A outflow: Silicon monoxide observations

The NGC 1333 IRAS 4A region was observed in the SiO v = 0 J = 1 -> 0 line with an angular resolution of about 2 ''. The SiO map revealed highly collimated outflows consisting of compact emission peaks. The map shows at least two outflows: the main bipolar outflow in the northeast-southwest direction and a shorter one toward the south. The main outflow displays a sharp bend in the middle of the northeastern lobe. The existence of a dense molecular cloud core just north of the bend suggests that the outflow may have been deflected as a result of jet-core collision. This explanation is also supported by the asymmetric morphology of the bipolar outflow, the good collimation and complicated kinematics of the deflected flow, the low-velocity emission from the molecular gas near the bend, and the enhancement of SiO emission in the deflected flow. The projected deflection angle is about 34 degrees, and a significant fraction of the kinetic energy of the outflow may have been transferred to the ambient cloud through the collision process. Since the main outflow is highly collimated, it was possible to identify the driving source. The longer main outflow is probably driven by IRAS 4A2, the secondary member of the protobinary system, and the shorter southern outflow by A1, the primary. Possible explanations for this anticorrelation between outflow and accretion include a delay of the onset of outflow activity in A1 and a reversal of accretion rates between binary components.