A Catalogue of Mid-infrared Variable Sources from unTimely

TL;DR

This paper presents the first large-scale catalog of mid-infrared variable sources from WISE data, identifying over 8 million variables and enabling new studies of diverse astrophysical phenomena in the mid-infrared.

Contribution

It introduces a comprehensive mid-infrared variability catalog using Bayesian methods, significantly expanding known variables and enabling discovery of rare astrophysical objects.

Findings

Over 8 million variable sources identified in W1 band

Detection of rare objects like eruptive young stars and active galactic nuclei

New dataset for mid-infrared time-domain astronomy

Abstract

The WISE and NEOWISE missions have provided the only mid-infrared all-sky time-domain data, opening a unique observational window for variability studies. Yet, a comprehensive and systematic catalog of mid-infrared variable sources has remained unavailable. In this work, we construct the first large-scale mid-infrared variability catalog based on the unTimely coadded photometry, covering tens of millions of sources. By employing a Bayesian Gaussian mixture model with a Dirichlet process, we identified 8,256,042 variable sources in the W1 band and 7,147,661 in the W2 band, significantly expanding the landscape of known mid-infrared variables. In addition to robust variability metrics, our analysis highlights rare and extreme outliers through dedicated outlier-detection algorithms, enabling the discovery of unusual classes of objects such as eruptive young stellar objects, highly variable active galactic nuclei, and other rare transients. This unprecedented dataset provides a new foundation for time-domain astronomy in the mid-infrared, offering complementary insights to optical and near-infrared surveys, and opening the door to systematic investigations of stellar evolution, accretion processes, and dust-enshrouded astrophysical environments on a Galactic and extragalactic scale.