Rotating Bullets from A Variable Protostar
  We present SMA CO(2-1) observations toward the protostellar jet driven by
SVS13A, a variable protostar in the NGC1333 star-forming region. The SMA
CO(2-1) images show an extremely high-velocity jet composed of a series of
molecular 'bullets'. Based on the SMA CO observations, we discover clear and
large systematic velocity gradients, perpendicular to the jet axis, in the
blueshifted and redshifted bullets. After discussing several alternative
interpretations, such as twin-jets, jet precession, warped disk, and internal
helical shock, we suggest that the systematic velocity gradients observed in
the bullets result from the rotation of the SVS13A jet. From the SMA CO images,
the measured rotation velocities are 11.7-13.7 km/s for the blueshifted bullet
and 4.7+/-0.5 km/s for the redshifted bullet. The estimated specific angular
momenta of the two bullets are comparable to those of dense cores, about 10
times larger than those of protostellar envelopes, and about 20 times larger
than those of circumstellar disks. If the velocity gradients are due to the
rotation of the SVS13A jet, the significant amount of specific angular momenta
of the bullets indicates that the rotation of jets/outflows is a key mechanism
to resolve the so-called 'angular momentum problem' in the field of star
formation. The kinematics of the bullets suggests that the jet launching
footprint on the disk has a radius of about 7.2-7.7 au, which appears to
support the extended disk-wind model. We note that further observations are
needed to comprehensively understand the kinematics of the SVS13A jet, in order
to confirm the rotation nature of the bullets.
