Origin of the ring structures in Hercules A

Astronomy and Astrophysics, vol. 658, pp. A5

Abstract

The prominent radio source Hercules A features complex structures in its radio lobes. Although it is one of the most comprehensively studied sources in the radio sky, the origin of the ring structures in the Hercules A radio lobes remains an open question. We present the first sub-arcsecond angular resolution images at low frequencies (<300 MHz) of Hercules A, made with the International LOFAR Telescope. With the addition of data from the Karl G. Jansky Very Large Array, we mapped the structure of the lobes from 144 MHz to 7 GHz. We explore the origin of the rings within the lobes of Hercules A, and test whether their properties are best described by a shock model, where shock waves are produced by the jet propagating in the radio lobe, or by an inner-lobe model, where the rings are formed by decelerated jetted plasma. From spectral index mapping our large frequency coverage reveals that the curvature of the different ring spectra increases with distance away from the central active galactic nucleus. We demonstrate that the spectral shape of the rings is consistent with synchrotron aging, which speaks in favor of an inner-lobe model where the rings are formed from the deposition of material from past periods of intermittent core activity.

Authors 21

1. R. Timmerman Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

2. Reinout J. van Weeren Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

3. J. R. Callingham Aachen Leiden Observatory

   Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, Dwingeloo, 7991 PD, The Netherlands

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

4. W. D. Cotton

   National Radio Astronomy Observatory

   Affiliation as printed

   National Radio Astronomy Obs, 520 Edgemont Rd., Charlottesville, VA 22903, USA

5. R. A. Perley

   National Radio Astronomy Observatory

   Affiliation as printed

   National Radio Astronomy Obs, PO Box 0, Socorro, NM 87801, USA

6. Leah K. Morabito

   Durham University

   Affiliation as printed

   Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham DH1 3LE, UK

   Institute for Computational Cosmology, Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK

7. Nectaria Gizani

   Hellenic Open University

   Affiliation as printed

   Hellenic Open University, School of Science & Technology, Parodos Aristotelous 18, Perivola Patron, Greece

8. A. H. Bridle

   National Radio Astronomy Observatory

   Affiliation as printed

   National Radio Astronomy Obs, 520 Edgemont Rd., Charlottesville, VA 22903, USA

9. C. P. O’Dea

   University of Manitoba

   Affiliation as printed

   Department of Physics & Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2, Canada

10. Stefi Alison Baum

    University of Manitoba

    Affiliation as printed

    Department of Physics & Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2, Canada

11. Grant R Tremblay

    Center for Astrophysics Harvard & Smithsonian

    Affiliation as printed

    Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA

12. Preeti Kharb

    National Centre for Radio Astrophysics · Savitribai Phule Pune University

    Affiliation as printed

    National Centre for Radio Astrophysics, S. P. Pune University Campus, Post Bag 3, Ganeshkhind Pune 411 007, India

13. N. E. Kassim

    Naval Research Laboratory Remote Sensing Division

    Affiliation as printed

    Remote Sensing Division, Naval Research Laboratory, Code 7213, 4555 Overlook Ave SW, Washington DC 20375, USA

14. Huub J. A. Röttgering Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

15. A. Botteon Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

16. Frits Sweijen Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

17. Cyril Tasse

    Centre National de la Recherche Scientifique · Rhodes University · Observatoire de Paris · Galaxies, Etoiles, Physique et Instrumentation · Université Paris Diderot

    Affiliation as printed

    Centre for Radio Astronomy Techniques and Technologies, Department of Physics and Electronics, Rhodes University, Grahamstown 6140, South Africa

    GEPI & USN, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France

18. M. Brüggen

    Universität Hamburg

    Affiliation as printed

    Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

19. J. Moldón

    Instituto de Astrofísica de Andalucía

    Affiliation as printed

    Instituto de Astrofísica de Andalucía (IAA, CSIC), Glorieta de las Astronomía, s/n, 18008 Granada, Spain

20. T. W. Shimwell Aachen Leiden Observatory

    Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy

    Affiliation as printed

    ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, Dwingeloo, 7991 PD, The Netherlands

    Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

21. G. Brunetti

    Istituto di Radioastronomia di Bologna

    Affiliation as printed

    INAF–Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy