Multi-epoch SMA observations of the L1448C(N) protostellar SiO jet

L1448C(N) is a young protostar in Perseus, driving an outflow and an extremely high-velocity (EHV) molecular jet. We present multi-epoch observations of SiO $J = 8-7$, CO $J = 3-2$ lines, and 345 GHz dust continuum toward L1448C(N) in 2006, 2010, and 2017 with the Submillimeter Array. The knots traced by the SiO line show the averaged proper motion is $\sim0''.06~{\rm yr^{-1}}$ and $\sim0''.04~{\rm yr^{-1}}$ for the blue- and red-shifted jet, respectively. The corresponding transverse velocities are $\sim78~{\rm km s^{-1}}$ (blueshifted) and $\sim52~{\rm km s^{-1}}$ (redshifted). Together with the radial velocity, we found the inclination angle of the jets from the plane of the sky to be $\sim34$\deg$$ for the blueshifted jet and $\sim46$\deg$$ for the redfshifted jet. Given the new inclination angles, the mass-loss rate and mechanical power were refined to be $\sim1.8\times 10^{-6}~M_\odot$ and $\sim1.3~L_\odot$, respectively. In the epoch of 2017, a new knot is detected at the base of the redshifted jet. We found that the mass-loss rate of the new knot is three times higher than the averaged mass-loss rate of the redshifted jet. Besides, continuum flux has enhanced by $\sim37\%$ between 2010 and 2017. These imply that the variation of the mass-accretion rate by a factor of $\sim3$ has occurred in a short timescale of $\sim10-20$ yr. In addition, a knot in the downstream of the redshifted jet is found to be dimming over the three epochs.