A VLBA Survey of radio stars in the Orion Nebula Cluster: I. The nonthermal radio population

TL;DR

This VLBA survey of the Orion Nebula Cluster identified 123 radio sources with nonthermal emission, revealing a population of deeply embedded young stellar objects and highlighting variability and detection challenges.

Contribution

First VLBA survey targeting all compact radio sources in the ONC, revealing nonthermal emission and deeply embedded young stellar objects not detectable in X-ray or near-infrared.

Findings

123 sources detected with VLBA counterparts

Many sources lack X-ray and near-infrared counterparts

High variability observed among sources

Abstract

We present first results of a four-epoch VLBA survey for nonthermal emission toward all 556 compact radio sources previously identified in a deep VLA survey of the Orion Nebula Cluster (ONC). We identify VLBA counterparts toward an unprecedented 123 sources. Of these, 41 do not have X-ray counterparts, of which 34 also do not display near-infrared counterparts. Since these cannot be explained by extragalactic background sources, this suggests a component of the ONC population of young stellar objects that are too deeply embedded for even X-rays to be detectable. We find pervasive variability and detect even most of the highest-S/N sources in only one out of four epochs. Neither a negative spectral index nor extreme variability in the VLA data is a good predictor of a VLBA detection.