A VLBA survey of radio stars in the Orion Nebula Cluster: III. Inter-epoch variability analysis
Abstract
We present a multi-epoch Very Long Baseline Array (VLBA) survey of radio sources in the Orion Nebula Cluster (ONC), updating the detection statistics and investigating inter-epoch variability. The dataset comprises eight C-band (4-8 GHz) epochs targeting 575 radio sources previously identified in deep Very Large Array surveys. VLBA observations result in resolutions of milliarcseconds and are only sensitive to high brightness temperatures meaning only non-thermal emission is observed. We detect 226 unique radio sources corresponding to a detection fraction of 39 per cent. The majority of sources (~83 per cent) are detected only once indicating that non-thermal emission associated with Young Stellar Objects (YSOs) is highly intermittent. To quantify variability, we use per-epoch peak flux densities and the variability factor (VF) defined as the ratio between the maximum and minimum fluxes. We identify 21 sources (~9 per cent of detected sources) that exhibit high variability defined as a change of flux density by at least a factor of five. We crossmatch with the COUP Chandra survey to identify sources as YSOs. We identify COUP counterparts for ~56 per cent of the detected sources. The remaining population cannot be explained solely by variability or background contamination, suggesting a population of radio detected YSOs without X-ray counterparts. We find a clear correlation between radio and X-ray luminosities consistent with the Güdel-Benz relation, the empirical relation between non-thermal radio and thermal X-ray emission for magnetically active stars.
Related
- Planetary Nebula Central Stars as Tracers of Planetary Nebula-Star Cluster Associations in the Galaxy
- Multi-branch classification of diffuse cluster radio emission from the LOFAR two-metre sky survey
- A Wolf-Rayet nebula in its disruption phase: high-resolution radio observations of PCG 11
- A Hectospec Spectroscopic Census of Kinematic Members in the Orion Nebula Cluster
- A Hectospec Spectroscopic Census of Kinematic Members in the Orion Nebula Cluster
BibTeX
@misc{okelly2026vlba,
title = {{A VLBA survey of radio stars in the Orion Nebula Cluster: III. Inter-epoch variability analysis}},
author = {E. T. O'Kelly and J. Forbrich and S. A. Dzib and J. Vargas-González},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.26466},
eprint = {2609.26466},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.26466},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A VLBA survey of radio stars in the Orion Nebula Cluster: III. Inter-epoch variability analysis
AU - E. T. O'Kelly
AU - J. Forbrich
AU - S. A. Dzib
AU - J. Vargas-González
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.26466
UR - https://arxiv.org/abs/2609.26466
AB - We present a multi-epoch Very Long Baseline Array (VLBA) survey of radio sources in the Orion Nebula Cluster (ONC), updating the detection statistics and investigating inter-epoch variability. The dataset comprises eight C-band (4-8 GHz) epochs targeting 575 radio sources previously identified in deep Very Large Array surveys. VLBA observations result in resolutions of milliarcseconds and are only sensitive to high brightness temperatures meaning only non-thermal emission is observed. We detect 226 unique radio sources corresponding to a detection fraction of 39 per cent. The majority of sources (~83 per cent) are detected only once indicating that non-thermal emission associated with Young Stellar Objects (YSOs) is highly intermittent. To quantify variability, we use per-epoch peak flux densities and the variability factor (VF) defined as the ratio between the maximum and minimum fluxes. We identify 21 sources (~9 per cent of detected sources) that exhibit high variability defined as a change of flux density by at least a factor of five. We crossmatch with the COUP Chandra survey to identify sources as YSOs. We identify COUP counterparts for ~56 per cent of the detected sources. The remaining population cannot be explained solely by variability or background contamination, suggesting a population of radio detected YSOs without X-ray counterparts. We find a clear correlation between radio and X-ray luminosities consistent with the Güdel-Benz relation, the empirical relation between non-thermal radio and thermal X-ray emission for magnetically active stars.
ER -