A Catalog of Mid-infrared Variable Sources in the Ecliptic Poles

TL;DR

This paper presents a catalog of mid-infrared variable sources near the ecliptic poles using NEOWISE data, revealing diverse sources including AGNs, stars, and obscured QSOs, with potential for future time-domain studies.

Contribution

The study provides the first extensive catalog of MIR variable sources at the ecliptic poles, including transient events linked to obscured QSOs, enhancing understanding of MIR variability.

Findings

Identified 2764 variables in NEP and 27581 in SEP.

Variability dominated by AGNs in NEP and stars in SEP.

Discovered three MIR transients associated with obscured QSOs.

Abstract

We construct a catalog of mid-infrared (MIR) variable sources using the multi-epoch 3.6 (W1) and 4.5 $\mu$m (W2) dataset from the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) at the north and south ecliptic poles (NEP and SEP). The catalog provides well-sampled light curves that cover areas within a radius of 5 degrees from the poles, which are frequently observed by current and forthcoming missions. By carefully processing the NEOWISE data to secure reliable photometric measurements, we identified 2764 and 27581 variables in the NEP and SEP, respectively, using the probability deviating from the non-variable and the correlation coefficient between W1 and W2. Cross-correlation with various complementary datasets reveals that, in the NEP, variability is dominated by active galactic nuclei, whereas stellar objects are more common in the SEP due to its proximity to the Large Magellanic Cloud. In particular, proper motion measurements from Gaia and MIR color-color diagrams are ideal for narrowing down the physical origin of the MIR variable sources. We identify three MIR transients in the NEP. Interestingly, all coincide with obscured QSOs, suggesting a physical connection between transient events and circumnuclear obscuration. Finally, we discuss the potential applications of our catalog in synergy with existing and future time-domain surveys.