The Quasar CTD 135 is Not a Compact Symmetric Object

TL;DR

This paper reclassifies the radio source CTD 135 from a candidate compact symmetric object to a blazar based on multi-wavelength observational evidence, challenging previous assumptions about its nature.

Contribution

The study provides a comprehensive re-evaluation of CTD 135's classification, emphasizing the importance of multi-wavelength data in distinguishing between CSOs and blazars.

Findings

CTD 135 exhibits a flat-spectrum radio core with high brightness temperature.

The source shows variability across multiple wavebands.

Infrared colors are consistent with blazar characteristics.

Abstract

The radio-loud quasar CTD 135 (2234+282, J2236+2828) has been proposed as a candidate compact symmetric object (CSO), based on its symmetric radio structure revealed by multi-frequency very long baseline interferometry (VLBI) imaging observations on milliarcsec angular scales. CSOs are known as young jetted active galactic nuclei (AGN) whose relativistic plasma jets are misaligned with respect to the line of sight. The peculiarity of CTD 135 as a CSO candidate was its detection in gamma-rays, while the vast majority of known gamma-ray emitting AGN are blazars with jets pointing close to our viewing direction. Since only a handful of CSOs are known as gamma-ray sources, the unambiguous identification of a single candidate is important for studying this rare class of objects. By collecting and interpreting observational data from the recent literature, we revisit the classification of CTD 135. We present evidence that the object, based on its flat-spectrum radio core with high brightness temperature, variability at multiple wavebands, and infrared colours should be classified as a blazar rather than a CSO