The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models
Using the new wideband capabilities of the ATCA, we obtain spectra for PKS 1718-649, a well-known gigahertzpeaked spectrum radio source. The observations, between approximately 1 and 10 GHz over 3 epochs spanning approximately 21 months, reveal variability both above the spectral peak at ~3 GHz and...
| 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/20.500.11937/44986 |
| _version_ | 1848757156567842816 |
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| author | Tingay, Steven Macquart, Jean-Pierre Collier, J. Rees, G. Callingham, J. Stevens, J. Carretti, E. Wayth, Randall Wong, G. Trott, C. McKinley, B. Bernardi, G. Bowman, J. Briggs, F. Cappallo, R. Corey, B. Deshpande, A. Emrich, D. Gaensler, B. Goeke, R. Greenhill, L. Hazelton, B. Johnston-Hollitt, M. Kaplan, D. Kasper, J. Kratzenberg, E. Lonsdale, C. Lynch, Mervyn McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Ord, Stephen Prabu, T. Rogers, A. Roshi, A. Shankar, N. Srivani, K. Subrahmanyan, R. Waterson, M. Webster, R. Whitney, A. Williams, A. Williams, C. |
| author_facet | Tingay, Steven Macquart, Jean-Pierre Collier, J. Rees, G. Callingham, J. Stevens, J. Carretti, E. Wayth, Randall Wong, G. Trott, C. McKinley, B. Bernardi, G. Bowman, J. Briggs, F. Cappallo, R. Corey, B. Deshpande, A. Emrich, D. Gaensler, B. Goeke, R. Greenhill, L. Hazelton, B. Johnston-Hollitt, M. Kaplan, D. Kasper, J. Kratzenberg, E. Lonsdale, C. Lynch, Mervyn McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Ord, Stephen Prabu, T. Rogers, A. Roshi, A. Shankar, N. Srivani, K. Subrahmanyan, R. Waterson, M. Webster, R. Whitney, A. Williams, A. Williams, C. |
| author_sort | Tingay, Steven |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Using the new wideband capabilities of the ATCA, we obtain spectra for PKS 1718-649, a well-known gigahertzpeaked spectrum radio source. The observations, between approximately 1 and 10 GHz over 3 epochs spanning approximately 21 months, reveal variability both above the spectral peak at ~3 GHz and below the peak. The combination of the low- and high-frequency variability cannot be easily explained using a single absorption mechanism, such as free-free absorption or synchrotron self-absorption. We find that the PKS 1718-649 spectrum and its variability are best explained by variations in the free-free optical depth on our line of sight to the radio source at low frequencies (below the spectral peak) and the adiabatic expansion of the radio source itself at high frequencies (above the spectral peak). The optical depth variations are found to be plausible when X-ray continuum absorption variability seen in samples of active galactic nuclei is considered. We find that the cause of the peaked spectrum in PKS 1718-649 is most likely due to free-free absorption. In agreement with previous studies, we find that the spectrum at each epoch of observation is best fit by a free-free absorption model characterized by a power-law distribution of free-free absorbing clouds. This agreement is extended to frequencies below the 1 GHz lower limit of the ATCA by considering new observations with Parkes at 725 MHz and 199 MHz observations with the newly operational Murchison Widefield Array. These lower frequency observations argue against families of absorption models (both free-free and synchrotron self-absorption) that are based on simple homogenous structures. |
| first_indexed | 2025-11-14T09:23:37Z |
| format | Journal Article |
| id | curtin-20.500.11937-44986 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T09:23:37Z |
| publishDate | 2015 |
| publisher | Institute of Physics Publishing |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-449862017-09-13T14:17:43Z The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models Tingay, Steven Macquart, Jean-Pierre Collier, J. Rees, G. Callingham, J. Stevens, J. Carretti, E. Wayth, Randall Wong, G. Trott, C. McKinley, B. Bernardi, G. Bowman, J. Briggs, F. Cappallo, R. Corey, B. Deshpande, A. Emrich, D. Gaensler, B. Goeke, R. Greenhill, L. Hazelton, B. Johnston-Hollitt, M. Kaplan, D. Kasper, J. Kratzenberg, E. Lonsdale, C. Lynch, Mervyn McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Ord, Stephen Prabu, T. Rogers, A. Roshi, A. Shankar, N. Srivani, K. Subrahmanyan, R. Waterson, M. Webster, R. Whitney, A. Williams, A. Williams, C. Using the new wideband capabilities of the ATCA, we obtain spectra for PKS 1718-649, a well-known gigahertzpeaked spectrum radio source. The observations, between approximately 1 and 10 GHz over 3 epochs spanning approximately 21 months, reveal variability both above the spectral peak at ~3 GHz and below the peak. The combination of the low- and high-frequency variability cannot be easily explained using a single absorption mechanism, such as free-free absorption or synchrotron self-absorption. We find that the PKS 1718-649 spectrum and its variability are best explained by variations in the free-free optical depth on our line of sight to the radio source at low frequencies (below the spectral peak) and the adiabatic expansion of the radio source itself at high frequencies (above the spectral peak). The optical depth variations are found to be plausible when X-ray continuum absorption variability seen in samples of active galactic nuclei is considered. We find that the cause of the peaked spectrum in PKS 1718-649 is most likely due to free-free absorption. In agreement with previous studies, we find that the spectrum at each epoch of observation is best fit by a free-free absorption model characterized by a power-law distribution of free-free absorbing clouds. This agreement is extended to frequencies below the 1 GHz lower limit of the ATCA by considering new observations with Parkes at 725 MHz and 199 MHz observations with the newly operational Murchison Widefield Array. These lower frequency observations argue against families of absorption models (both free-free and synchrotron self-absorption) that are based on simple homogenous structures. 2015 Journal Article http://hdl.handle.net/20.500.11937/44986 10.1088/0004-6256/149/2/74 Institute of Physics Publishing fulltext |
| spellingShingle | Tingay, Steven Macquart, Jean-Pierre Collier, J. Rees, G. Callingham, J. Stevens, J. Carretti, E. Wayth, Randall Wong, G. Trott, C. McKinley, B. Bernardi, G. Bowman, J. Briggs, F. Cappallo, R. Corey, B. Deshpande, A. Emrich, D. Gaensler, B. Goeke, R. Greenhill, L. Hazelton, B. Johnston-Hollitt, M. Kaplan, D. Kasper, J. Kratzenberg, E. Lonsdale, C. Lynch, Mervyn McWhirter, S. Mitchell, D. Morales, M. Morgan, E. Oberoi, D. Ord, Stephen Prabu, T. Rogers, A. Roshi, A. Shankar, N. Srivani, K. Subrahmanyan, R. Waterson, M. Webster, R. Whitney, A. Williams, A. Williams, C. The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models |
| title | The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models |
| title_full | The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models |
| title_fullStr | The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models |
| title_full_unstemmed | The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models |
| title_short | The spectral variability of the GHz-peaked spectrum radio source PKS 1718-649 and a comparison of absorption models |
| title_sort | spectral variability of the ghz-peaked spectrum radio source pks 1718-649 and a comparison of absorption models |
| url | http://hdl.handle.net/20.500.11937/44986 |