High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars
Journal
Date Issued
2016
Author(s)
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D'Abrusco, R.
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Burlon, D.
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Hurley-Walker, N.
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Johnston-Hollitt, M.
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Morgan, J.
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Pavlidou, V.
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Bell, M.
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•
Bhat, R.
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Bowman, J. D.
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Briggs, F.
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Cappallo, R. J.
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Corey, B. E.
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Deshpande, A. A.
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Ewall-Rice, A.
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Emrich, D.
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Gaensler, B. M.
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Goeke, R.
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Greenhill, L. J.
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Hazelton, B. J.
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Hindson, L.
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Kaplan, D. L.
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Kasper, J. C.
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Kratzenberg, E.
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Feng, L.
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Jacobs, D.
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Kudryavtseva, N.
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Lenc, E.
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Lonsdale, C. J.
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Lynch, M. J.
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McKinley, B.
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McWhirter, S. R.
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Mitchell, D. A.
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Morales, M. F.
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Morgan, E.
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Oberoi, D.
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Offringa, A. R.
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Ord, S. M.
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Pindor, B.
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Prabu, T.
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Procopio, P.
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Riding, J.
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Rogers, A. E. E.
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Roshi, A.
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Udaya Shankar, N.
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Srivani, K. S.
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Subrahmanyan, R.
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Tingay, S. J.
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Waterson, M.
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Wayth, R. B.
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Webster, R. L.
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Whitney, A. R.
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Williams, A.
•
Williams, C. L.
Abstract
Context. Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies.
Aims: We characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources.
Methods: We cross-correlated the 6100 deg2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detected by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue.
Results: We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120-180 MHz) blazar spectral index is ⟨αlow⟩ = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources.
Conclusions: Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population. Tables 5-7 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A141
Aims: We characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources.
Methods: We cross-correlated the 6100 deg2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detected by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue.
Results: We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120-180 MHz) blazar spectral index is ⟨αlow⟩ = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources.
Conclusions: Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population. Tables 5-7 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A141
Volume
588
Start page
A141
Issn Identifier
0004-6361
Ads BibCode
2016A&A...588A.141G
Rights
open.access
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