X-ray Through Very-High-Energy Intrabinary Shock Emission from Black Widows and Redbacks

TL;DR

This paper models X-ray and gamma-ray emissions from black widow and redback binary systems, constraining key parameters and predicting high-energy fluxes, with implications for future gamma-ray observatories.

Contribution

It introduces a multi-zone spectral model for intrabinary shocks in spider binaries, enabling detailed parameter constraints and flux predictions.

Findings

Constrained magnetic field and plasma flow speed in PSR J1723--2837.

Predicted high-energy gamma-ray fluxes for nearby spider systems.

Identified potential targets for future Cherenkov Telescope Array observations.

Abstract

Black widow and redback systems are compact binaries in which a millisecond pulsar heats and may even ablate its low-mass companion by its intense wind of relativistic particles and radiation. In such systems, an intrabinary shock can form as a site of particle acceleration and associated non-thermal emission. We model the X-ray and gamma-ray synchrotron and inverse-Compton spectral components for select spider binaries, including diffusion, convection and radiative energy losses in an axially-symmetric, steady-state approach. Our new multi-zone code simultaneously yields energy-dependent light curves and orbital phase-resolved spectra. Using parameter studies and matching the observed X-ray spectra and light curves, and Fermi Large Area Telescope spectra where available, with a synchrotron component, we can constrain certain model parameters. For PSR J1723--2837 these are notably the magnetic field and bulk flow speed of plasma moving along the shock tangent, the shock acceleration efficiency, and the multiplicity and spectrum of pairs accelerated by the pulsar. This affords a more robust prediction of the expected high-energy and very-high-energy gamma-ray flux. We find that nearby pulsars with hot or flaring companions may be promising targets for the future Cherenkov Telescope Array. Moreover, many spiders are likely to be of significant interest to future MeV-band missions such as AMEGO and e-ASTROGAM.