Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421
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 th...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Journal Article |
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Institute of Physics Publishing
2015
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| Online Access: | http://hdl.handle.net/20.500.11937/30927 |
| _version_ | 1848753231083077632 |
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| author | Callingham, J. Gaensler, B. Ekers, R. Tingay, Steven Wayth, Randall Morgan, J. Bernardi, G. Bell, M. Bhat, R. Bowman, J. Briggs, F. Cappallo, R. Deshpande, A. Ewall-Wice, A. Feng, L. Greenhill, L. Hazelton, B. Hindson, L. Hurley-Walker, N. Jacobs, D. Johnston-Hollitt, M. Kaplan, D. Kudrayvtseva, N. Lenc, E. Lonsdale, C. McKinley, B. McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Offringa, A. Ord, S. Pindor, B. Prabu, T. Procopio, P. Riding, J. Srivani, K. Subrahmanyan, R. Shankar, N. Webster, R. Williams, A. Williams, C. |
| author_facet | Callingham, J. Gaensler, B. Ekers, R. Tingay, Steven Wayth, Randall Morgan, J. Bernardi, G. Bell, M. Bhat, R. Bowman, J. Briggs, F. Cappallo, R. Deshpande, A. Ewall-Wice, A. Feng, L. Greenhill, L. Hazelton, B. Hindson, L. Hurley-Walker, N. Jacobs, D. Johnston-Hollitt, M. Kaplan, D. Kudrayvtseva, N. Lenc, E. Lonsdale, C. McKinley, B. McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Offringa, A. Ord, S. Pindor, B. Prabu, T. Procopio, P. Riding, J. Srivani, K. Subrahmanyan, R. Shankar, N. Webster, R. Williams, A. Williams, C. |
| author_sort | Callingham, J. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | 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. |
| first_indexed | 2025-11-14T08:21:13Z |
| format | Journal Article |
| id | curtin-20.500.11937-30927 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T08:21:13Z |
| publishDate | 2015 |
| publisher | Institute of Physics Publishing |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-309272019-02-19T05:35:23Z Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421 Callingham, J. Gaensler, B. Ekers, R. Tingay, Steven Wayth, Randall Morgan, J. Bernardi, G. Bell, M. Bhat, R. Bowman, J. Briggs, F. Cappallo, R. Deshpande, A. Ewall-Wice, A. Feng, L. Greenhill, L. Hazelton, B. Hindson, L. Hurley-Walker, N. Jacobs, D. Johnston-Hollitt, M. Kaplan, D. Kudrayvtseva, N. Lenc, E. Lonsdale, C. McKinley, B. McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Offringa, A. Ord, S. Pindor, B. Prabu, T. Procopio, P. Riding, J. Srivani, K. Subrahmanyan, R. Shankar, N. Webster, R. Williams, A. Williams, C. 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. 2015 Journal Article http://hdl.handle.net/20.500.11937/30927 10.1088/0004-637X/809/2/168 Institute of Physics Publishing fulltext |
| spellingShingle | Callingham, J. Gaensler, B. Ekers, R. Tingay, Steven Wayth, Randall Morgan, J. Bernardi, G. Bell, M. Bhat, R. Bowman, J. Briggs, F. Cappallo, R. Deshpande, A. Ewall-Wice, A. Feng, L. Greenhill, L. Hazelton, B. Hindson, L. Hurley-Walker, N. Jacobs, D. Johnston-Hollitt, M. Kaplan, D. Kudrayvtseva, N. Lenc, E. Lonsdale, C. McKinley, B. McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Offringa, A. Ord, S. Pindor, B. Prabu, T. Procopio, P. Riding, J. Srivani, K. Subrahmanyan, R. Shankar, N. Webster, R. Williams, A. Williams, C. Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421 |
| title | Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421 |
| title_full | Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421 |
| title_fullStr | Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421 |
| title_full_unstemmed | Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421 |
| title_short | Broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source PKS B0008-421 |
| title_sort | broadband spectral modeling of the extreme gigahertz-peaked spectrum radio source pks b0008-421 |
| url | http://hdl.handle.net/20.500.11937/30927 |