# A Matched Filter Technique For Slow Radio Transient Detection And First Demonstration With The Murchison Widefield Array

## TL;DR

This paper introduces a novel matched filter technique for detecting slow radio transients directly from image time series, demonstrating its effectiveness with Murchison Widefield Array data and setting new upper limits on transient surface density.

## Contribution

The paper develops a temporal matched filter method for radio transient detection that surpasses traditional source-finding approaches, especially in confusion-limited regimes.

## Key findings

- Technique effectively detects transients despite confusion noise.
- No transients detected in the observed data, setting new upper limits.
- Method applicable to various instruments and timescales.

## Abstract

Many astronomical sources produce transient phenomena at radio frequencies, but the transient sky at low frequencies (<300 MHz) remains relatively unexplored. Blind surveys with new widefield radio instruments are setting increasingly stringent limits on the transient surface density on various timescales. Although many of these instruments are limited by classical confusion noise from an ensemble of faint, unresolved sources, one can in principle detect transients below the classical confusion limit to the extent that the classical confusion noise is independent of time. We develop a technique for detecting radio transients that is based on temporal matched filters applied directly to time series of images rather than relying on source-finding algorithms applied to individual images. This technique has well-defined statistical properties and is applicable to variable and transient searches for both confusion-limited and non-confusion-limited instruments. Using the Murchison Widefield Array as an example, we demonstrate that the technique works well on real data despite the presence of classical confusion noise, sidelobe confusion noise, and other systematic errors. We searched for transients lasting between 2 minutes and 3 months. We found no transients and set improved upper limits on the transient surface density at 182 MHz for flux densities between ~20--200 mJy, providing the best limits to date for hour- and month-long transients.