Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz
© 2018 The Author(s). We useMurchisonWidefieldArray(MWA) observations of interplanetary scintillation (IPS) to determine the source counts of point (< 0.3 arcsec extent) sources and of all sources with some subarcsecond structure, at 162 MHz. We have developed the methodology to derive these...
| Main Authors: | , , , , |
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| Format: | Journal Article |
| Published: |
Oxford University Press
2018
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| Online Access: | http://hdl.handle.net/20.500.11937/71877 |
| _version_ | 1848762597654921216 |
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| author | Chhetri, Rajan Ekers, Ronald Morgan, John Macquart, Jean-Pierre Franzen, Thomas |
| author_facet | Chhetri, Rajan Ekers, Ronald Morgan, John Macquart, Jean-Pierre Franzen, Thomas |
| author_sort | Chhetri, Rajan |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | © 2018 The Author(s). We useMurchisonWidefieldArray(MWA) observations of interplanetary scintillation (IPS) to determine the source counts of point (< 0.3 arcsec extent) sources and of all sources with some subarcsecond structure, at 162 MHz. We have developed the methodology to derive these counts directly from the IPS observables, while taking into account changes in sensitivity across the survey area. The counts of sources with compact structure follow the behaviour of the dominant source population above ~3 Jy but below this they show Euclidean behaviour. We compare our counts to those predicted by simulations and find a good agreement for our counts of sources with compact structure, but significant disagreement for point source counts. Using low radio frequency spectral energy distributions (SEDs) from the Galactic and Extragalactic MWA survey, we classify point sources as compact steep spectrum (CSS), flat spectrum, or peaked. If we consider the CSS sources to be the more evolved counterparts of the peaked sources, the two categories combined comprise approximately 80 per cent of the point source population. We calculate densities of potential calibrators brighter than 0.4 Jy at low frequencies and find 0.2 sources per square degrees for point sources, rising to 0.7 sources per square degree if sources with more complex arcsecond structure are included. We extrapolate to estimate 4.6 sources per square degrees at 0.04 Jy. We find that a peaked spectrum is an excellent predictor for compactness at low frequencies, increasing the number of good calibrators by a factor of three compared to the usual flat spectrum criterion. |
| first_indexed | 2025-11-14T10:50:06Z |
| format | Journal Article |
| id | curtin-20.500.11937-71877 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T10:50:06Z |
| publishDate | 2018 |
| publisher | Oxford University Press |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-718772019-01-22T01:21:26Z Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz Chhetri, Rajan Ekers, Ronald Morgan, John Macquart, Jean-Pierre Franzen, Thomas © 2018 The Author(s). We useMurchisonWidefieldArray(MWA) observations of interplanetary scintillation (IPS) to determine the source counts of point (< 0.3 arcsec extent) sources and of all sources with some subarcsecond structure, at 162 MHz. We have developed the methodology to derive these counts directly from the IPS observables, while taking into account changes in sensitivity across the survey area. The counts of sources with compact structure follow the behaviour of the dominant source population above ~3 Jy but below this they show Euclidean behaviour. We compare our counts to those predicted by simulations and find a good agreement for our counts of sources with compact structure, but significant disagreement for point source counts. Using low radio frequency spectral energy distributions (SEDs) from the Galactic and Extragalactic MWA survey, we classify point sources as compact steep spectrum (CSS), flat spectrum, or peaked. If we consider the CSS sources to be the more evolved counterparts of the peaked sources, the two categories combined comprise approximately 80 per cent of the point source population. We calculate densities of potential calibrators brighter than 0.4 Jy at low frequencies and find 0.2 sources per square degrees for point sources, rising to 0.7 sources per square degree if sources with more complex arcsecond structure are included. We extrapolate to estimate 4.6 sources per square degrees at 0.04 Jy. We find that a peaked spectrum is an excellent predictor for compactness at low frequencies, increasing the number of good calibrators by a factor of three compared to the usual flat spectrum criterion. 2018 Journal Article http://hdl.handle.net/20.500.11937/71877 10.1093/mnras/sty1665 Oxford University Press restricted |
| spellingShingle | Chhetri, Rajan Ekers, Ronald Morgan, John Macquart, Jean-Pierre Franzen, Thomas Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz |
| title | Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz |
| title_full | Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz |
| title_fullStr | Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz |
| title_full_unstemmed | Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz |
| title_short | Interplanetary scintillation studies with the Murchison Widefield Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162MHz |
| title_sort | interplanetary scintillation studies with the murchison widefield array iii: comparison of source counts and densities for radio sources and their sub-arcsecond components at 162mhz |
| url | http://hdl.handle.net/20.500.11937/71877 |