Sulentic, J. W.J. W.SulenticMartínez-Carballo, M. A.M. A.Martínez-CarballoMARZIANI, PaolaPaolaMARZIANI0000-0002-6058-4912del Olmo, A.A.del OlmoSTIRPE, Giovanna MariaGiovanna MariaSTIRPE0000-0002-3702-8731Zamfir, S.S.ZamfirPlauchu-Frayn, I.I.Plauchu-Frayn2020-03-182020-03-1820150035-8711http://hdl.handle.net/20.500.12386/23369We acknowledge Dra Simona Righini for observations in INAF–IRA radiotelescope station in Medicina (Italy). We would like to thank Drs Jaime Perea and Isabel Márquez for all the fruitful discussions on the subject and their help with the observations. We also thank the anonymous referee for many useful comments which helped to significantly improve the presentation of our analysis. Part of this work was supported by Junta de Andalucía through grant TIC-114 and by the Spanish Ministry for Science and Innovation through grants AYA2010-15169, AYA2011-1544-E and AYA2013-42227-P. This research is based in part on data obtained with the 1.82-m Copernico Telescope at the Asiago Observatory. Based partially on observations made with the 3.5-m telescope at the Spanish-German Observatory in Calar Alto (CAHA, Almerí­a Spain) jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofí­sica de Andalucí­a (CSIC). We thank all the CAHA staff for their high professionalism and support with the observations. Some data presented here were obtained with ALFOSC, which is provided by the Instituto de Astrofísica de Andalucía (IAA) under a joint agreement with the University of Copenhagen and NOTSA.Lobe-dominated radio-loud (LD RL) quasars occupy a restricted domain in the 4D Eigenvector 1 (4DE1) parameter space which implies restricted geometry/physics/kinematics for this subclass compared to the radio-quiet (RQ) majority of quasars. We discuss how this restricted domain for the LD RL parent population supports the notion for a RQ-RL dichotomy among type 1 sources. 3C 57 is an atypical RL quasar that shows both uncertain radio morphology and falls in a region of 4DE1 space where RL quasars are rare. We present new radio flux and optical spectroscopic measures designed to verify its atypical optical/UV spectroscopic behaviour and clarify its radio structure. The former data confirms that 3C 57 falls off the 4DE1 quasar `main sequence' with both extreme optical Fe II emission (R_{Fe II} ̃ 1) and a large C IV λ1549 profile blueshift (̃-1500 km s<SUP>-1</SUP>). These parameter values are typical of extreme Population A sources which are almost always RQ. New radio measures show no evidence for flux change over a 50+ year time-scale consistent with compact steep-spectrum (or young LD) over core-dominated morphology. In the 4DE1 context where LD RL are usually low L/L<SUB>Edd</SUB> quasars, we suggest that 3C 57 is an evolved RL quasar (i.e. large blackhole mass) undergoing a major accretion event leading to a rejuvenation reflected by strong Fe II emission, perhaps indicating significant heavy metal enrichment, high bolometric luminosity for a low-redshift source and resultant unusually high Eddington ratio giving rise to the atypical C IV λ1549.STAMPAenArticle10.1093/mnras/stv7102-s2.0-84938149112000356338500061https://academic.oup.com/mnras/article/450/2/1916/9833452015MNRAS.450.1916SFIS/05 - ASTRONOMIA E ASTROFISICA