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Origin of the ring structures in Hercules A. Sub-arcsecond 144 MHz to 7 GHz observations

Timmerman, R.; van Weeren, R.J.; Callingham, J.R.; Cotton, W.D.; Perley, R.; Morabito, L.K.; Gizani, N.A.B.; Bridle, A.H.; O'Dea, C.P.; Baum, S.A.; Tremblay, G.R.; Kharb, P.; Kassim, N.E.; Röttgering, H.J.A.; Botteon, A.; Sweijen, F.; Tasse, C.; Brüggen, M.; Moldon, J.; Shimwell, T.; Brunetti, G.

Origin of the ring structures in Hercules A. Sub-arcsecond 144 MHz to 7 GHz observations Thumbnail


Authors

R. Timmerman

R.J. van Weeren

J.R. Callingham

W.D. Cotton

R. Perley

N.A.B. Gizani

A.H. Bridle

C.P. O'Dea

S.A. Baum

G.R. Tremblay

P. Kharb

N.E. Kassim

H.J.A. Röttgering

A. Botteon

F. Sweijen

C. Tasse

M. Brüggen

J. Moldon

T. Shimwell

G. Brunetti



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.

Citation

Timmerman, R., van Weeren, R., Callingham, J., Cotton, W., Perley, R., Morabito, L., …Brunetti, G. (2022). Origin of the ring structures in Hercules A. Sub-arcsecond 144 MHz to 7 GHz observations. Astronomy & Astrophysics, 658, Article A5. https://doi.org/10.1051/0004-6361/202140880

Journal Article Type Article
Acceptance Date Jul 1, 2021
Online Publication Date Jan 25, 2022
Publication Date 2022-02
Deposit Date Oct 5, 2021
Publicly Available Date Oct 22, 2021
Journal Astronomy and astrophysics.
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 658
Article Number A5
DOI https://doi.org/10.1051/0004-6361/202140880

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Copyright Statement
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.






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