  PSR J1023+0038 is an exceptional system for understanding how slowly rotating
neutron stars are spun up to millisecond rotational periods through accretion
from a companion star. Observed as a radio pulsar from 2007-2013, optical data
showed that the system had an accretion disk in 2000/2001. Starting at the end
of 2013 June, the radio pulsar has become undetectable, suggesting a return to
the previous accretion-disk state, where the system more closely resembles an
X-ray binary. In this Letter we report the first targeted X-ray observations
ever performed of the active phase and complement them with UV/Optical and
radio observations collected in 2013 October. We find strong evidence that
indeed an accretion disk has recently formed in the system and we report the
detection of fast X-ray changes spanning about two orders of magnitude in
luminosity. No radio pulsations are seen during low flux states in the X-ray
light-curve or at any other times.
