The long-term optical flux variations of Compact Symmetric Objects

TL;DR

This study investigates the long-term optical flux and color variability of Compact Symmetric Objects (CSOs) and compares them with blazars, revealing that CSOs have lower variability but share similar color change patterns with blazars, linked to jet activity.

Contribution

First comprehensive analysis of optical flux and color variability in CSOs over 5 years, comparing with blazars to understand jet-related variability mechanisms.

Findings

CSOs exhibit lower optical variability than blazars.

Both CSOs and blazars show a bluer-when-brighter color trend.

Variability is attributed to relativistic jets and beaming effects.

Abstract

Compact Symmetric Objects (CSOs) are a distinct category of jetted active galactic nuclei (AGN) whose optical variability characteristics have not been well investigated. We present here the results of our investigation on the optical flux and colour variability properties of a bona fide sample of 38 CSOs. We used the g-, r- and i-bands data from the Zwicky Transient Facility survey that spans a duration of about 5 years. We also considered a comparison sub-sample of blazars that includes 5 flat spectrum radio quasars and 12 BL Lac objects with redshifts and g-band magnitudes similar to the limited sub-sample of 9 CSOs. These two sub-samples of AGN, chosen for this comparative study of their long-term optical variability, represent different orientations of their relativistic jets with respect to the observer. We found that both CSOs and blazars exhibit optical flux variations, although variability of CSOs is lower than that of blazars. The observed variability in both CSOs and blazars is attributed to the relativistic jets and the increased optical variations in blazars relative to CSOs are likely due to beaming effects. CSOs and blazars exhibit similar colour variations, with both of them showing a bluer when brighter trend. Such a colour variability pattern is expected due to processes associated with their relativistic jets.