A Search for Radio Transients in VLA Archival Images of the 3C 286 Field

TL;DR

This study conducted a comprehensive search for radio transients in archival VLA data of 3C 286 over 23 years, finding no transients but setting upper limits on their surface density at various flux levels.

Contribution

First systematic search for radio transients in the VLA archive of the 3C 286 field, establishing new upper limits on transient surface density.

Findings

No transients detected in 23 years of data.

Set upper limits on transient surface density at different flux levels.

Future archival searches could improve sensitivity by 1-2 orders of magnitude.

Abstract

We present a search for radio transients in the field of the bright radio source 3C 286 using archival observations from the Very Large Array. These observations span 23 years and include 1852 epochs at 1.4 GHz in the C and D configurations. We find no transients in the field. The sensitivity of the observations is limited by dynamic range effects in the images. At large flux densities ($> 0.2$ Jy), single epoch observations provide a strong limit on the transient surface density. At flux densities near the dynamic range threshold, we use the requirement that transient sources must appear in consecutive epochs to be confirmed as real. This sets the sensitivity at low flux densities to transient durations of $\tau \sim 1$ day, while $\tau > 1$ minute for high flux densities. At 70 mJy, we find a 1-$\sigma$ limit on the surface density $\Sigma < 3 \times 10^{-3}$ deg$^{-2}$. At 3 Jy, we find a 1-$\sigma$ limit $\Sigma < 9 \times 10^{-4}$ deg$^{-2}$. A future systematic search of the VLA archives can provide one to two orders of magnitude more sensitivity to radio transients.