MeV and TeV Emission from Millisecond Pulsar Binaries

Black widow (BW) and redback (RB) systems are compact binaries in which a millisecond pulsar heats its low-mass companion by its intense wind of relativistic particles and emission. Radio and optical follow-up of unidentified Fermi Large Area Telescope (LAT) sources has expanded the number of these systems from four to nearly 30. Orbital modulation in X-rays observed in many systems suggests an intrabinary shock exists as a site for particle acceleration, which in many instances wraps around the pulsar. We model the broadband spectral components from nearby `spider binaries', including diffusion, convection and radiative energy losses of shock-accelerated particles in an axially-symmetric, steady-state approach. The resulting spectra comprise two main components: synchrotron radiation from X-rays to soft gamma rays and inverse-Compton emission at TeV energies from scattering thermal photons from the companion star. Two sources, J1723-2837 (RB) and J1311-3430 (BW), have been observed by Fermi-LAT, leading to constraints on the maximum particle energy and particle acceleration in these mini pulsar wind nebulae. We find that nearby binaries in a `flaring state' are promising targets for H.E.S.S. and the future Cherenkov Telescope Array and that GeV photons may be detectable by Fermi-LAT. Moreover, some of these systems will be excellent targets for future MeV missions such as AMEGO.