{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T02:50:31Z","timestamp":1760151031497,"version":"build-2065373602"},"reference-count":42,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2022,2,4]],"date-time":"2022-02-04T00:00:00Z","timestamp":1643932800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Hungarian National Research, Development and Innovation Office","award":["OTKA K134213","2018-2.1.14-T\u00c9T-CN-2018-00001"],"award-info":[{"award-number":["OTKA K134213","2018-2.1.14-T\u00c9T-CN-2018-00001"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>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 \u03b3-rays, while the vast majority of known \u03b3-ray emitting AGN are blazars with jets pointing close to our viewing direction. Since only a handful of CSOs are known as \u03b3-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.<\/jats:p>","DOI":"10.3390\/sym14020321","type":"journal-article","created":{"date-parts":[[2022,2,6]],"date-time":"2022-02-06T20:40:18Z","timestamp":1644180018000},"page":"321","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["The Quasar CTD 135 Is Not a Compact Symmetric Object"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3079-1889","authenticated-orcid":false,"given":"S\u00e1ndor","family":"Frey","sequence":"first","affiliation":[{"name":"Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Mikl\u00f3s \u00fat 15-17, H-1121 Budapest, Hungary"},{"name":"Institute of Physics, ELTE E\u00f6tv\u00f6s Lor\u00e1nd University, P\u00e1zm\u00e1ny P\u00e9ter S\u00e9t\u00e1ny 1\/A, H-1117 Budapest, Hungary"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1020-1597","authenticated-orcid":false,"given":"Krisztina \u00c9.","family":"Gab\u00e1nyi","sequence":"additional","affiliation":[{"name":"Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Mikl\u00f3s \u00fat 15-17, H-1121 Budapest, Hungary"},{"name":"Department of Astronomy, Institute of Geography and Earth Sciences, ELTE E\u00f6tv\u00f6s Lor\u00e1nd University, P\u00e1zm\u00e1ny P\u00e9ter S\u00e9t\u00e1ny 1\/A, H-1117 Budapest, Hungary"},{"name":"ELKH-ELTE Extragalactic Astrophysics Research Group, ELTE E\u00f6tv\u00f6s Lor\u00e1nd University, P\u00e1zm\u00e1ny P\u00e9ter S\u00e9t\u00e1ny 1\/A, H-1117 Budapest, Hungary"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4341-0029","authenticated-orcid":false,"given":"Tao","family":"An","sequence":"additional","affiliation":[{"name":"Shanghai Astronomical Observatory, Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China"}]}],"member":"1968","published-online":{"date-parts":[[2022,2,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"L87","DOI":"10.1086\/187518","article-title":"Two-sided Ejection in Powerful Radio Sources: The Compact Symmetric Objects","volume":"432","author":"Wilkinson","year":"1994","journal-title":"Astrophys. 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