VVV-WIT-04: an extragalactic variable source caught by the VVV Survey

TL;DR

This paper reports the discovery of VVV-WIT-04, a highly variable near-infrared source likely of extragalactic origin, identified through the VVV survey, with characteristics consistent with an OVV quasar.

Contribution

First identification of a highly variable extragalactic source in near-infrared data from the VVV survey, suggesting its nature as an OVV quasar.

Findings

VVV-WIT-04 is a highly variable near-IR source.

The variability matches that of an OVV quasar.

Alternative transient scenarios are inconsistent with data.

Abstract

We report the discovery of VVV-WIT-04, a near-infrared variable source towards the Galactic disk located ~0.2 arcsec apart from the position of the radio source PMN J1515-5559. The object was found serendipitously in the near-IR data of the ESO public survey VISTA Variables in the V\'ia L\'actea (VVV). Our analysis is based on variability, multicolor, and proper motion data from VVV and VVV eXtended surveys, complemented with archive data at longer wavelengths. We suggest that VVV-WIT-04 has an extragalactic origin as the near-IR counterpart of PMN J1515-5559. The Ks-band light-curve of VVV-WIT-04 is highly variable and consistent with that of an Optically Violent Variable (OVV) quasar. The variability in the near-IR can be interpreted as the redshifted optical variability. Residuals to the proper motion varies with the magnitude suggesting contamination by a blended source. Alternative scenarios, including a transient event such as a nova or supernova, or even a binary microlensing event are not in agreement with the available data.