Pulsar Radiative Heating in Black Widow Binaries

In the black widow binaries a millisecond pulsar (MSP) strongly heats a sub-stellar companion in a close (P_b ~ few hour) orbit. Multicolor optical photometry can be used to study this heating pattern. By fitting such data to specific heating models, one may constrain the binary geometry including the important companion Roche lobe fill factor and the orbitalinclination.We report here on new multicolor photometry of four black widow binaries (PSRs J0023+0923, J0952-0607, J1124-3653 and J2241-5236) collected from a variety of telescopes, with 2m to 10m aperture. We fit this with our implementation of the ICARUS binary modeling code, measuring the binary parameters. In particular we focus on the MSP heating power. Since the observed MSP radiation is dominated by GeV gamma-rays, we compare this heating power, which is directed at the orbital/spin equator, with the observed Fermi flux, which is directed at inclination i. This ratio can be compared with predictions ofpulsar beaming models, such as the `outer gap' picture.This work was supported in part by NASA grants 80NSSC17K0502 and 80NSSC17K0024.