VLBA Observations of Strong Anisotripic Radio Scattering towards the Orion Nebula

TL;DR

This paper reports VLBA observations of a radio source near the Orion Nebula, revealing strong, anisotropic scattering likely caused by ionized gas from massive star winds, and suggests the source is extragalactic.

Contribution

First detailed VLBA imaging of a heavily scattered, anisotropic radio source near Orion, linking scattering properties to local ionized stellar winds.

Findings

Source is extragalactic based on spectral energy distribution.

Scattering disk size follows a ν^{-2} dependence.

Scattering is highly anisotropic with a 2:1 axis ratio.

Abstract

We present observations of VLBA 20, a radio source found towards the edge of the Orion Nebula Cluster (ONC). Nonthermal emission dominates the spectral energy distribution of this object from radio to mid-infrared regime, suggesting that VLBA 20 is extragalactic. This source is heavily scattered in the radio regime. Very Long Baseline Array observations resolve it to ~34x19 mas at 5 GHz, and the wavelength dependence of the scattering disk is consistent with $\nu^{-2}$ at other frequencies. The origin of the scattering is most likely the ionized X-ray emitting gas from the winds of the most massive stars of the ONC. The scattering is highly anisotropic, with the axis ratio of 2:1, higher than what is typically observed towards other sources.