Issue |
A&A
Volume 588, April 2016
|
|
---|---|---|
Article Number | A146 | |
Number of page(s) | 10 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201527404 | |
Published online | 01 April 2016 |
The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447
II. The radio view⋆
1
Lehrstuhl für Astronomie, Universität Würzburg,
Campus Hubland Nord, Emil-Fischer-Str.
31,
97074
Würzburg,
Germany
e-mail:
robert.schulz@physik.uni-wuerzburg.de
2
Dr. Remeis-Sternwarte & ECAP, Universität
Erlangen-Nürnberg, Sternwartstr.
7, 96049
Bamberg,
Germany
3
NASA, Goddard Space Flight Center, 8800 Greenbelt
Rd, Greenbelt,
MD
20771,
USA
4
University of Maryland, Baltimore County, 1000 Hilltop Cir,
Baltimore, MD
21250,
USA
5
The Catholic University of America, 620 Michigan Ave NE, Washington, DC
20064,
USA
6
Max-Planck-Institut für Radioastronomie,
Auf dem Hügel 69, 53121
Bonn,
Germany
7
Observatori Astronòmic, Univ. València, 46980
Paterna València,
Spain
8
Dept. Astronomia i Astrofìsica, Univ. València, 46100
Burjassot, València,
Spain
9
CSIRO, Astronomy and Space Science, ATNF, PO Box 76
Epping,
NSW
1710,
Australia
10
Max-Planck-Institut für extraterrestrische Physik,
Giessenbachstrasse 1,
85741
Garching,
Germany
11
Bundesamt für Kartographie und Geodäsie,
93444
Bad Kötzingen,
Germany
12
CSIRO Astronomy and Space Science, Canberra Deep Space
Communications Complex, PO Box 1035, Tuggeranong
ACT
2901,
Australia
13
School of Mathematics & Physics, University of
Tasmania, Private Bag 37,
Hobart, 7001
Tasmania,
Australia
14
University of California, San Diego, CASS, 9500 Gilman Dr., MC 0424,
La Jolla, CA
92093-0424,
USA
15
Department of Astrophysics/MAPP, Radboud University
Nijmegen, PO Box
9010, 6500 GL
Nijmegen, The
Netherlands
16
Hartebeesthoek Radio Astronomy Observatory,
1740
Krugersdorp, South
Africa
Received: 18 September 2015
Accepted: 25 October 2015
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.
Key words: galaxies: active / galaxies: individual: PKS 2004-447 / radio continuum: galaxies / techniques: interferometric / galaxies: jets
The VLBI images shown in Figs. 3 and 4 (as FITS files) and the ATCA data listed in Table A.1 are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A146
© ESO, 2016
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