High-energy sources at low radio frequency : the Murchison Widefield Array view of Fermi blazars

Giroletti, M., Massaro, F., D'Abrusco, R., Lico, R., Burlon, D., Hurley-Walker, N., Johnston-Hollitt, M., Morgan, J., Pavlidou, V., Bell, M., Bernardi, G., Bhat, R., Bowman, J. D., Briggs, F., Cappallo, R. J., Corey, B. E., Deshpande, A. A., Ewall-Rice, A., Emrich, D., Gaensler, B. M., Goeke, R., Greenhill, L. J., Hazelton, B. J., Hindson, L., Kaplan, D. L., Kasper, J. C., Kratzenberg, E., Feng, L., Jacobs, D., Kurdryavtseva, N., Lenc, E., Lonsdale, C. J., Lynch, M. 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., Rogers, A. E. E., Roshi, A., Shankar, N. Udaya, Srivani, K. S., Subrahmanyan, R., Tingay, S. J., Waterson, M., Wayth, R. B., Webster, R. L., Whitney, A. R., Williams, A. and Williams, C. L. (2016) High-energy sources at low radio frequency : the Murchison Widefield Array view of Fermi blazars. Astronomy & Astrophysics, 588: A141. ISSN 0004-6361

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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. 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. We cross-correlated the 6,100 deg^2 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 \fermilat. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. 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 $\langle \alpha_\mathrm{low} \rangle=0.57\pm0.02$: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at $\sim$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. 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.

Item Type	Article
Identification Number	10.1051/0004-6361/201527817
Additional information	This is the accepted version of the following article: Giroletti, M. et al., A&A, 588 (2016) A141, which has been published in final form at DOI: http://dx.doi.org/10.1051/0004-6361/201527817. This article may be used for non-commercial purposes in accordance with the EDP Sciences self-archiving policies.
Keywords	astro-ph.he
Date Deposited	15 May 2025 13:10
Last Modified	18 Feb 2026 20:15