  We report on X-ray observations of the young, energetic radio pulsar PSR
J1105-6107 obtained using the Rossi X-ray Timing Explorer. Our timing analysis
of Proportional Counter Array data finds no evidence for X-ray pulsations from
this source. We set a new upper limit on the pulsed X-ray flux from the pulsar
of 18% in the 2-10 keV band, for a duty cycle of 0.5. Our improved upper limit
supports the hypothesis that the X-ray emission seen by the ASCA X-ray
satellite in the direction of PSR J1105-6107 is the result of a pulsar-powered
synchrotron nebula.
