The Allen Telescope Array Twenty-centimeter Survey -- A 700-Square-Degree, Multi-Epoch Radio Dataset -- II: Individual Epoch Transient Statistics

TL;DR

This paper presents a detailed analysis of the ATATS radio survey, providing new constraints on transient source populations and demonstrating the survey's capabilities in detecting bright radio transients over a large sky area.

Contribution

It introduces a multi-epoch, wide-field radio survey dataset and establishes new upper limits on transient source rates at 1.4 GHz, improving understanding of transient populations.

Findings

Fewer than 6e-4 transients per square degree brighter than 350 mJy.

The combined image has RMS noise of 3.96 mJy/beam.

The survey rules out the previously reported high-rate transient sources.

Abstract

We present our second paper on the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch, ~700 sq. deg. radio image and catalog at 1.4 GHz. The survey is designed to detect rare, bright transients as well as to commission the ATA's wide-field survey capabilities. ATATS explores the challenges of multi-epoch transient and variable source surveys in the domain of dynamic range limits and changing (u,v) coverage. Here we present images made using data from the individual epochs, as well as a revised image combining data from all ATATS epochs. The combined image has RMS noise 3.96 mJy / beam, with a circular beam of 150 arcsec FWHM. The catalog, generated using a false detection rate algorithm, contains 4984 sources, and is >90% complete to 37.9 mJy. The catalogs generated from snapshot images of the individual epochs contain between 1170 and 2019 sources over the 564 sq. deg. area in common to all epochs. The 90% completeness limits of the single epoch catalogs range from 98.6 to 232 mJy. We compare the catalog generated from the combined image to those from individual epochs, and from the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency. We are able to place new constraints on the transient population: fewer than 6e-4 transients / sq. deg., for transients brighter than 350 mJy with characteristic timescales of minutes to days. This strongly rules out an astronomical origin for the ~1 Jy sources reported by Matsumura et al. (2009), based on their stated rate of 3.1e-3 / sq. deg.