Extended Non-Thermal Emission Possibly Associated with Cyg OB2 #5

TL;DR

This paper reports the detection of extended non-thermal radio emission near Cyg OB2 #5, suggesting it may be related to shock-accelerated electrons from stellar wind interactions or an unrelated background source.

Contribution

First detection of extended non-thermal emission near Cyg OB2 #5, exploring possible origins including stellar wind shocks or background sources.

Findings

Detection of ~30" extended non-thermal radio emission.

Possible association with shock-accelerated electrons from stellar winds.

Alternative explanation as background radio source.

Abstract

Cyg OB2 #5 is a contact binary system (O6.5-7+O5.5-6) with associated radio continuum emission. Two compact ($\leq 0\rlap.{"}3$) radio continuum components have been reported previously: the primary one is associated with the contact binary and the secondary one is an arc-like source $\sim 0\rlap.{"}8$ to the NE of the primary. This arc-like source results from the interaction of the winds of the contact binary and a B-type star in the region. In this paper we report the detection of an extended ($\sim 30"$), non-thermal component to the NE of the compact components. We propose that this extended emission could be an unresolved background source (i. e. a radio galaxy), extended galactic emission, or non-thermal emission related with relativistic electrons that are produced in the shock between the contact binary and the B-type star and that are carried away to large distances by the wind from the contact binary.