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The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447: II. the radio view


Schulz, R and Kreikenbohm, A and Kadler, M and Ojha, R and Ros, E and Stevens, J and Edwards, PG and Carpenter, B and Elsasser, D and Gehrels, N and Grossberger, C and Hase, H and Horiuchi, S and Lovell, JEJ and Mannheim, K and Markowitz, A and Mueller, C and Phillips, C and Ploetz, C and Quick, J and Truestedt, J and Tzioumis, AK and Wilms, J, The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447: II. the radio view, Astronomy and Astrophysics, 588 Article A146. ISSN 0004-6361 (2016) [Refereed Article]


Copyright Statement

Copyright ESO 2016

DOI: doi:10.1051/0004-6361/201527404


Context: Γ-ray-detected radio-loud narrow-line Seyfert 1 (γ-NLS1) galaxies constitute a small but interesting sample of the γ-ray-loud AGN. The radio-loudest γ-NLS1 known, PKS 2004−447, is located in the southern hemisphere and is monitored in the radio regime by the multiwavelength monitoring programme TANAMI.

Aims: We aim for the first detailed study of the radio morphology and long-term radio spectral evolution of PKS 2004−447, which are essential for understanding the diversity of the radio properties of γ-NLS1s.

Methods: The TANAMI VLBI monitoring program uses the Australian Long Baseline Array (LBA) and telescopes in Antarctica, Chile, New Zealand, and South Africa to monitor the jets of radio-loud active galaxies in the southern hemisphere. Lower resolution radio flux density measurements at multiple radio frequencies over four years of observations were obtained with the Australia Telescope Compact Array (ATCA).

Results: The TANAMI VLBI image at 8.4 GHz shows an extended one-sided jet with a dominant compact VLBI core. Its brightness temperature is consistent with equipartition, but it is an order of magnitude below other γ-NLS1s with the sample value varying over two orders of magnitude. We find a compact morphology with a projected large-scale size < 11 kpc and a persistent steep radio spectrum with moderate flux-density variability.

Conclusions: PKS 2004−447 appears to be a unique member of the γ-NLS1 sample. It exhibits blazar-like features, such as a flat featureless X-ray spectrum and a core-dominated, one-sided parsec-scale jet with indications for relativistic beaming. However, the data also reveal properties atypical for blazars, such as a radio spectrum and large-scale size consistent with compact-steep-spectrum (CSS) objects, which are usually associated with young radio sources. These characteristics are unique among all γ-NLS1s and extremely rare among γ-ray-loud AGN.

Item Details

Item Type:Refereed Article
Keywords:galaxies: active galaxies: individual: PKS 2004-447 radio continuum: galaxies techniques: interferometric galaxies: jets
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:High energy astrophysics and galactic cosmic rays
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Lovell, JEJ (Dr Jim Lovell)
ID Code:115225
Year Published:2016
Web of Science® Times Cited:21
Deposited By:Mathematics and Physics
Deposited On:2017-03-10
Last Modified:2018-04-11
Downloads:125 View Download Statistics

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