J/MNRAS/485/1822ivo://CDS.VizieR/J/MNRAS/485/1822doi:10.26093/cds/vizier.74851822CDSPlavin A.V.Kovalev Y.Y.Pushkarev A.B.Lobanov A.P.2024-08-19T20:17:12Z2019-08-29T07:51:52ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fractive-galactic-nucleiThe apparent position of jet base (core) in radio-loud active galactic nuclei changes with frequency because of synchrotron self-absorption. Studying this 'core shift' effect enables us to reconstruct properties of the jet regions close to the central engine. We report here results from core shift measurements in AGNs observed with global VLBI at 2 and 8GHz at epochs from 1994 to 2016. Our sample contains 40 objects observed at least 10 times during that period. The core shift is determined using a new automatic procedure introduced to minimize possible biases. The resulting multiple epoch measurements of the core position are employed for examining temporal variability of the core shift. We argue that the core shift variability is a common phenomenon, as established for 33 of 40 AGNs we study. Our analysis shows that the typical offsets between the core positions at 2 and 8GHz are about 0.5mas and they vary in time. Typical variability of the individual core positions is about 0.3mas. The measurements show a strong dependence between the core position and its flux density, suggesting that changes in both are likely related to the nuclear flares injecting denser plasma into the flow. We determine that density of emitting relativistic particles significantly increases during these flares, while relative magnetic field changes less and in the opposite direction.2019MNRAS.485.1822Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/485/1822CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/485/1822https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/485/1822http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/485/1822https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/485/1822https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/485/1822http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/485/1822GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/485/1822/table1 (Source properties)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/485/1822/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/485/1822/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/485/1822/table1?GETtext/xml+votable180.050000true1.557887222-6.3931486940.0055555555555555566/556 911 2836 3024 4027 4695 5423 5767 6548 6641 9676 10163 10422 11430 11715 12241 13156 13496 13927 15494 16298 17351 18506 18661 19190 21266 21968 22917 23099 24084 25503 27060 27583 27765 28479 29016 31664 43822 44247 46964https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/485/1822?format=asciidefaultJ/MNRAS/485/1822/table1Source propertiesSimbadNameSimbad column added by the CDSmeta.idcharB1950B1950 name (HHMM+DDd)meta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ2000J2000 name from Radio Fundamental Catalogue (RFC, http://astrogeo.org/rfc) version 2017c (JHHMM+DDMM)meta.id;meta.maincharRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainzRedshift from Lister et al. (2009, Cat. J/AJ/137/3718)src.redshiftfloatPAjet positional angle estimated as described in Section 2degpos.posAngfloatNobsNumber of observational epochs used in our analysismeta.numberintJ/MNRAS/485/1822/table2Estimated parameter valuesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ2000J2000 name from RFC (JHHMM+DDMM)meta.id;meta.maincharObs.dateEpoch of observationtime.epochnullableCoreShiftmas8-2GHz core shift magnitude in milliarcsecondsmaspos.angDistancedoubleCoreShiftpc8-2GHz core shift magnitude in parsecs (projected on the sky)pcpos.distancedouble