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.
