Investigation of the broadband emission of the gamma-ray binary HESS J0632+057 using an intrabinary shock model

TL;DR

This study models the broadband X-ray and gamma-ray emissions of the gamma-ray binary HESS J0632+057 using an intrabinary shock framework, successfully reproducing key observational features and revealing the need for additional emission components.

Contribution

It introduces a detailed intrabinary shock model that explains the observed spectral and light curve features of HESS J0632+057, including phase-dependent emission components.

Findings

Reproduced X-ray and TeV light curve features with the IBS model.

Identified TeV peaks as inverse-Compton and Doppler-beamed emissions.

Discovered phase-resolved SEDs require an extra ICS component from pre-shock particles.

Abstract

We investigated a wealth of X-ray and gamma-ray spectral energy distribution (SED) and multi-band light curve (LC) data of the gamma-ray binary HESS J0632+057 using a phenomenological intrabinary shock (IBS) model. Our baseline model assumes that the IBS is formed by colliding winds from a putative pulsar and its Be companion, and particles accelerated in the IBS emit broadband radiation via synchrotron (SY) and inverse-Compton upscattering (ICS) processes. Adopting the latest orbital solution and system geometry (Tokayer et al. 2021), we reproduced the global X-ray and TeV LC features, two broad bumps at $\phi \sim 0.3$ and $\sim0.7$, with the SY and ICS model components. We found these TeV LC peaks originate from ICS emission caused by the enhanced seed photon density near periastron and superior conjunction or Doppler-beamed emission of bulk-accelerated particles in the IBS at inferior conjunction. While our IBS model successfully explained most of the observed SED and LC data, we found that phase-resolved SED data in the TeV band require an additional component associated with ICS emission from pre-shock particles (produced by the pulsar wind). This finding indicates a possibility of delineating the IBS emission components and determining the bulk Lorentz factors of the pulsar wind at certain orbital phases.