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http://hdl.handle.net/20.500.12386/24700
Titolo: | Broadband Spectral Modeling of the Extreme Gigahertz-peaked Spectrum Radio Source PKS B0008-421 | Autori: | Callingham, J. R. Gaensler, B. M. Ekers, R. D. Tingay, S. J. Wayth, R. B. Morgan, J. BERNARDI, GIANNI Bell, M. E. Bhat, R. Bowman, J. D. Briggs, F. Cappallo, R. J. Deshpande, A. A. Ewall-Wice, A. Feng, L. Greenhill, L. J. Hazelton, B. J. Hindson, L. Hurley-Walker, N. Jacobs, D. C. Johnston-Hollitt, M. Kaplan, D. L. Kudrayvtseva, N. Lenc, E. Lonsdale, C. J. McKinley, B. McWhirter, S. R. Mitchell, D. A. Morales, M. F. Morgan, E. Oberoi, D. Offringa, A. R. Ord, S. M. Pindor, B. Prabu, T. Procopio, P. Riding, J. Srivani, K. S. Subrahmanyan, R. Udaya Shankar, N. Webster, R. L. Williams, A. Williams, C. L. |
Data pubblicazione: | 2015 | Rivista: | THE ASTROPHYSICAL JOURNAL | Numero: | 809 | Fascicolo: | 2 | Da pagina:: | 168 | Abstract: | We present broadband observations and spectral modeling of PKS B0008-421 and identify it as an extreme gigahertz-peaked spectrum (GPS) source. PKS B0008-421 is characterized by the steepest known spectral slope below the turnover, close to the theoretical limit of synchrotron self-absorption, and the smallest known spectral width of any GPS source. Spectral coverage of the source spans from 0.118 to 22 GHz, which includes data from the Murchison Widefield Array and the wide bandpass receivers on the Australia Telescope Compact Array. We have implemented a Bayesian inference model fitting routine to fit the data with internal free-free absorption (FFA), single- and double-component FFA in an external homogeneous medium, FFA in an external inhomogeneous medium, or single- and double-component synchrotron self-absorption models, all with and without a high-frequency exponential break. We find that without the inclusion of a high-frequency break these models cannot accurately fit the data, with significant deviations above and below the peak in the radio spectrum. The addition of a high-frequency break provides acceptable spectral fits for the inhomogeneous FFA and double-component synchrotron self-absorption models, with the inhomogeneous FFA model statistically favored. The requirement of a high-frequency spectral break implies that the source has ceased injecting fresh particles. Additional support for the inhomogeneous FFA model as being responsible for the turnover in the spectrum is given by the consistency between the physical parameters derived from the model fit and the implications of the exponential spectral break, such as the necessity of the source being surrounded by a dense ambient medium to maintain the peak frequency near the gigahertz region. This implies that PKS B0008-421 should display an internal H i column density greater than 10<SUP>20</SUP> cm<SUP>-2</SUP>. The discovery of PKS B0008-421 suggests that the next generation of low radio frequency surveys could reveal a large population of GPS sources that have ceased activity, and that a portion of the ultra-steep-spectrum source population could be composed of these GPS sources in a relic phase. | Acknowledgments: | The authors thank Geoffrey Bicknell, David Jauncey, and Edward King for stimulating discussions about the theoretical aspects of the absorption models and the VLBI measurements of PKS B0008-421. This scientific work makes use of the Murchison Radioastronomy Observatory, operated by CSIRO. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. Support for the MWA comes from the U.S. National Science Foundation (grants AST-0457585, PHY-0835713, CAREER-0847753, and AST-0908884), the Australian Research Council (LIEF grants LE0775621 and LE0882938), the U.S. Air Force Office of Scientific Research (grant FA9550-0510247), and the Centre for All-sky Astrophysics (an Australian Research Council Centre of Excellence funded by grant CE110001020). Support is also provided by the Smithsonian Astrophysical Observatory, the MIT School of Science, the Raman Research Institute, the Australian National University, and the Victoria University of Wellington (via grant MED-E1799 from the New Zealand Ministry of Economic Development and an IBM Shared University Research Grant). The Australian federal government provides additional support via the CSIRO, National Collaborative Research Infrastructure Strategy, Education Investment Fund, the Australia India Strategic Research Fund, and Astronomy Australia Limited, under contract to Curtin University. We acknowledge the iVEC Petabyte Data Store, the Initiative in Innovative Computing and the CUDA Center for Excellence sponsored by NVIDIA at Harvard University, and the International Centre for Radio Astronomy Research (ICRAR), a Joint Venture of Curtin University and the University of Western Australia, funded by the Western Australian State government. The Australia Telescope Compact Array is part of the Australia Telescope National Facility, which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. This paper includes archived data obtained through the Australia Telescope Online Archive ( http://atoa.atnf.csiro.au ). This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. | URI: | http://hdl.handle.net/20.500.12386/24700 | URL: | https://iopscience.iop.org/article/10.1088/0004-637X/809/2/168 | ISSN: | 0004-637X | DOI: | 10.1088/0004-637X/809/2/168 | Bibcode ADS: | 2015ApJ...809..168C | Fulltext: | open |
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