Phase-reference mapping of a weak-cored double-lobed source in the 1636+473 system using MERLIN and Global VLBI |
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| Authors: | M. J. Rioja R. W. Porcas S. Garrington A. Alberdi D. J. Saikia |
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| Affiliation: | 1. INAF/IAPS - Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere I-00133, Roma, Italy;2. Dipartimento di Fisica e Astronomia, Alma Mater Studiorum, Università degli Studi di Bologna, Via Gobetti 93/2, 40129 Bologna, Italy;3. INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, I-40129 Bologna, Italy;4. Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332-0430, United States;5. Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland;6. TAPIR, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA;7. Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy;8. INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy;9. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany;10. Centre for Extragalactic Astronomy, Durham University, South Road, Durham, DH1 3LE, UK;11. Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze, Via. G. Sansone 1, I-50019 Sesto Fiorentino (FI), Italy;12. INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy;13. Joint Institute for VLBI ERIC, Oude Hoogeveensedijk 4, 7991 PD, Dwingeloo, The Netherlands;14. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA;15. Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA;p. School of Physics and Astronomy and Institute of Gravitational Wave Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom;q. Universitäts-Sternwarte München, Scheinerstr.1, D-81679 München, Germany;r. Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy;s. Sorbonne Universites et CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, F-75014 Paris, France;t. Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege M. út 15–17, H-1121 Budapest, Hungary;u. MTA-ELTE Extragalactic Astrophysics Research Group, ELTE TTK Pázmány Péter sétány 1/A, H-1117 Budapest, Hungary;v. Department of Astronomy, Eötvös Loránd University, Pázmány Péter sétány 1/A, H-1117 Budapest, Hungary;w. Centro de Astrobiología (CSIC-INTA), Departamento de Astrofísica; Camino Bajo del Castillo s/n, Villanueva de la Cañada, E-28692 Madrid, Spain;x. ESA - European Space Agency. ESTEC, Keplerlaan 1 2201AZ Noordwijk, The Netherlands;y. Department of Astronomy, Columbia University, New York, NY 10027, USA;z. Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstrasse 150, 44801 Bochum, Germany;1. European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile;2. Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Magrans, E-08193 Barcelona, Spain;3. ICREA & Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Barcelona 08028, Spain;4. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China;5. SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands;6. Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands;7. XMM-Newton SOC, ESAC/ESA, E-28692 Villanueva de la Cañada, Madrid, Spain;8. Instituto de Astrofísica de Andalucía (IAA-CSIC), E-18008, Granada, Spain;9. INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone (Roma), Italy |
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| Abstract: | We present maps and astrometric results from first epoch, simultaneous MERLIN and Global VLBI observations of the very weak core of a double-lobed radio source, using as reference the bright, compact, flat-spectrum quasar 1636+473 A, 20 arcsec away. The observations were made in May 1995 at 5 GHz. The phase-referenced VLBI map of the weak core, of resolution 1.5 mas, contains a high percentage of the core flux density seen in the MERLIN map. Further hybrid mapping iterations reveal a faint, one-sided core extension on the same side as the MERLIN jet. We explore the effect of both temporal and other coherence losses on the phase-reference map. We relate our results to the structural asymmetry in weak AGN cores within the context of unification models. |
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| Keywords: | Astrometry Galaxies: active Galaxies: jets Methods: data analysis Quasars: general Techniques: interferometry |
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