Commensal Transient Searches in Eight Short Gamma Ray Burst Fields

TL;DR

This study utilizes MeerKAT radio telescope observations to perform commensal transient searches in short gamma-ray burst fields, identifying variable sources and constraining transient rates at different flux levels.

Contribution

It demonstrates the effectiveness of commensal transient searches with MeerKAT and provides new upper limits on transient rates in short gamma-ray burst fields.

Findings

122 variable sources detected, mostly AGN and possibly flaring stars.

Most variability attributed to interstellar scintillation.

Upper limits set on transient rates at specified flux and fluence levels.

Abstract

A new generation of radio telescopes with excellent sensitivity, instantaneous {\it uv} coverage, and large fields of view, are providing unprecedented opportunities for performing commensal transient searches. Here we present such a commensal search in deep observations of short gamma-ray burst fields carried out with the MeerKAT radio telescope in South Africa at 1.3 GHz. These four hour observations of eight different fields span survey lengths of weeks to months. We also carry out transient searches in time slices of the full observations, at timescales of 15 minutes, and 8 seconds. We find 122 variable sources on the long timescales, of which 52 are likely active galactic nuclei, but there are likely also some radio flaring stars. While the variability is intrinsic in at least two cases, most of it is consistent with interstellar scintillation. In this study, we also place constraints on transient rates based on state-of-the-art transient simulations codes. We place an upper limit of $2\times10^{-4}$ transients per day per square degree for transients with peak flux of 5 mJy, and an upper limit of $2.5\times10^{-2}$ transients per day per square degree for transients with a fluence of 10 Jy ms, the minimum detectable fluence of our survey.