Intrabinary Shock Emission from Black Widows and Redbacks
  Eclipsing millisecond pulsars in close ($P_b < 1$~day) binary systems provide
a different view of pulsar winds and shocks than do isolated pulsars. Since
2009, the numbers of these systems known in the Galactic field has increased
enormously. We have been systematically studying many of these newly discovered
systems at multiple wavelengths. Typically, the companion is nearly Roche-lobe
filling and heated by the pulsar which drives mass loss from the companion. The
pulsar wind shocks with this material just above the surface of the companion.
We discuss various observational properties of this shock, including radio
eclipses, orbitally modulated X-ray emission, and the potential for
$\gamma$-ray emission. Redbacks, whose companions are likely non-degenerate and
significantly more massive, generally have more luminous shocks than black
widows which have very low mass companions. This is expected since the more
massive redback companions intercept a greater fraction of the pulsar wind. We
also compare these systems to accreting millisecond pulsars, which may be
progenitors of black widows and in some cases can pass back and forth between
redback and accretion phases.
