# Gamma Rays from colliding winds in massive binaries. Status and prospects

## TL;DR

This paper reviews the physics and observational signatures of gamma-ray emission from colliding wind binaries, highlighting the case of HD 93129A and the potential of upcoming multi-wavelength observations during its 2018 periastron passage.

## Contribution

It provides a concise overview of the current understanding of gamma-ray production in colliding wind binaries and discusses the prospects for future observational campaigns.

## Key findings

- Gamma-ray emission is linked to particle acceleration in colliding wind binaries.
- HD 93129A is a key system for studying gamma-ray production.
- Upcoming observations during periastron will enhance understanding of these phenomena.

## Abstract

Binary systems formed by early-type stars with strong winds are known to display variable non-thermal radio emission, thermal X-rays, and, at least in one case (Eta Carina), $\gamma$ rays. Some of these systems are quite eccentric and the conditions for efficient particle acceleration and $\gamma$-ray production might manifest only occasionally. In this paper I briefly review the physics of colliding wind binaries with emphasis on the observational signatures of non-thermal particle acceleration. I discuss, in particular, the case of the system HD 93129A which is made up by an O2 If* star (the primary) and an O3.5 V star (the secondary). The primary is among the earliest, hottest, most massive, luminous, and windy O stars in the Galaxy. The periastron passage during 2018 will offer an outstanding observational window that will be exploited by an international multi-wavelength campaign.