The low mass companions of evaporating binary pulsars ( black widows and their ilk ) are strongly heated on the side facing the pulsar .
However in high-quality photometric and spectroscopic data the heating pattern does not match that expected for direct pulsar illumination .
Here we explore heating mediated by an intra-binary shock ( IBS ) .
We develop a simple analytic model and implement it in the popular ‘ ICARUS ’ light curve code .
The model is parameterized by the wind momentum ratio \beta and velocity v _ { Rel } v _ { orb } and assumes that the reprocessed pulsar wind emits prompt particles or radiation to heat the companion surface .
We illustrate an interesting range of light curve asymmetries controlled by these parameters .
The code also computes the IBS synchrotron emission pattern , and thus can model black widow X-ray light curves .
As a test we apply the results to the high quality asymmetric optical light curves of PSR J2215+5135 ; the resulting fit gives a substantial improvement upon direct heating models and produces an X-ray light curve consistent with that seen .
The IBS model parameters imply that , at the present loss rate , the companion evaporation has a characteristic timescale \tau _ { evap } \approx 150 My .
Still , the model is not fully satisfactory , indicating additional unmodeled physical effects .