The Fermi LAT view of the colliding wind binaries

TL;DR

This study analyzes nearly 7 years of Fermi-LAT data on seven colliding wind binaries, detecting gamma-ray emission from WR 11 and setting upper limits for others, advancing understanding of high-energy processes in these systems.

Contribution

The paper provides the first gamma-ray detection of WR 11 and offers constraints on other CWBs, using extensive Fermi-LAT data and theoretical modeling to identify promising candidates.

Findings

WR 11 detected at 6.1σ confidence level

Gamma-ray luminosity of WR 11 measured as ~3.7×10^31 erg/s

Upper limits established for WR 70 and WR 140

Abstract

Colliding wind binaries (CWBs) have been considered as a possible high energy $\gamma$-ray sources for some time, however no system other than $\eta$ Car has been detected. In the paper a sample of seven CWBs (WR 11, WR 70, WR 137, WR 140, WR 146, WR 147) which, by means of theoretic modelling, were deemed most promising candidates, was analyzed using almost 7 years of the Fermi-LAT data. WR 11 ($\gamma^2$ Vel) was detected at 6.1$\sigma$ confidence level with a photon flux in 0.1-100 GeV range $(1.8\pm0.6)\times10^{-9}~\mathrm{ph~cm^{-2}~s^{-1}}$ and an energy flux $(2.7\pm0.5)\times10^{-12}~~\mathrm{erg~cm^{-2}~s^{-1}}$. At the adopted distance $d=340$ pc this corresponds to a luminosity $L=(3.7\pm0.7)\times10^{31}~\mathrm{erg~s^{-1}}$. This luminosity amounts to $\sim6\times10^{-6}$ fraction of the total wind kinetic power and $\sim1.6\times10^{-4}$ fraction of the power injected into the wind-wind interaction region of this system. Upper limits were set on the high energy flux from the WR 70 and WR 140 systems.