Extragalactic transient candidates in the Second Swift-XRT Point Source catalogue

TL;DR

This paper utilizes the Second Swift-XRT Point Source catalogue to identify and analyze extragalactic transient candidates, recovering known sources and discovering new ones with diverse properties, enhancing transient detection methods.

Contribution

The study introduces a systematic approach for transient detection in the Swift-XRT catalogue, including methodology for identifying new sources and assessing their spectral characteristics.

Findings

Recovered 167 known transients

Discovered 19 new transient candidates

Estimated 65% completeness in detection

Abstract

The Second Swift-XRT Point Source catalogue offers a combination of sky coverage and sensitivity and presents an invaluable opportunity for transient discovery. We search the catalogue at the positions of inactive and active galaxies, and identify transient candidates by comparison with XMM-Newton and ROSAT. We recover 167 previously known transients and find 19 sources consistent with being new sources, estimating a completeness of $\sim65\%$. These 19 new sources are split approximately equally between inactive and active hosts and their peak X-ray luminosities span $\sim 10^{42} - 10^{47}$ erg s$^{-1}$. We find eight are best fit with non-thermal spectral models and one with a blackbody. We also discuss our methodology and its application to the forthcoming Living Swift-XRT Point Source catalogue for the potential near real time serendipitous discovery of $\sim$ few new X-ray transients per year.