# Extreme radio flares and associated X-ray variability from young stellar objects in the Orion Nebula Cluster

## TL;DR

This study presents simultaneous radio and X-ray observations of young stellar objects in the Orion Nebula Cluster, revealing extreme radio flares with some correlating to X-ray variability on short timescales, offering new insights into high-energy processes in YSOs.

## Contribution

The paper provides the first simultaneous deep radio and X-ray observations targeting hundreds of YSOs to quantify extreme radio flare occurrence and their correlation with X-ray variability.

## Key findings

- 13 sources showed extreme radio variability with flux changes over an hour.
- Some radio flares correlated with X-ray variability on sub-hour timescales.
- Strong X-ray variability alone does not predict extreme radio flares.

## Abstract

Young stellar objects are known to exhibit strong radio variability on timescales of weeks to months, and a few reports have documented extreme radio flares, with at least an order of magnitude change in flux density on timescales of hours to days. However, there have been few constraints on the occurrence rate of such radio flares or on the correlation with pre-main sequence X-ray flares, although such correlations are known for the Sun and nearby active stars. Here we report simultaneous deep VLA radio and Chandra X-ray observations of the Orion Nebula Cluster, targeting hundreds of sources to look for the occurrence rate of extreme radio variability and potential correlation with the most extreme X-ray variability. We identify 13 radio sources with extreme radio variability, with some showing an order of magnitude change in flux density in less than 30 minutes. All of these sources show X-ray emission and variability, but only on timescales <1h do we find clear correlations with extreme radio flaring. Strong X-ray variability does not predict the extreme radio sources and vice versa. Radio flares thus provide us with a new perspective on high-energy processes in YSOs and the irradiation of their protoplanetary disks. Finally, our results highlight implications for interferometric imaging of sources violating the constant-sky assumption.