Multi-wavelength Optical and NIR Variability Analysis of the Blazar PKS 0027-426

TL;DR

This study analyzes multi-wavelength optical and NIR variability of the blazar PKS 0027-426, revealing complex spectral behaviors and inter-band lags that suggest simultaneous or closely timed emission regions.

Contribution

It provides a detailed multi-wavelength variability analysis of PKS 0027-426, including cross-correlation and spectral behavior over multiple years, which is novel for this blazar.

Findings

Inter-band lags suggest simultaneous or closely timed emission.

Complex color-brightness relationships vary over time.

Spectral analysis reveals changing color behaviors.

Abstract

We present multi-wavelength spectral and temporal variability analysis of PKS 0027-426 using optical griz observations from DES (Dark Energy Survey) between 2013-2018 and VOILETTE (VEILS Optical Light curves of Extragalactic TransienT Events) between 2018-2019 and near infrared (NIR) JKs observations from VEILS (VISTAExtragalactic Infrared Legacy Survey) between 2017-2019. Multiple methods of cross-correlation of each combination of light curve provides measurements of possible lags between optical-optical, optical-NIR, and NIR-NIR emission, for each observation season and for the entire observational period. Inter-band time lag measurements consistently suggest either simultaneous emission or delays between emission regions on timescales smaller than the cadences of observations. The colour-magnitude relation between each combination of filters was also studied to determine the spectral behaviour of PKS 0027-426. Our results demonstrate complex colour behaviour that changes between bluer when brighter (BWB), stable when brighter (SWB) and redder when brighter (RWB) trends over different timescales and using different combinations of optical filters. Additional analysis of the optical spectra is performed to provide further understanding of this complex spectral behaviour.