Modelling of the spectral energy distribution of Fornax A: leptonic and hadronic production of high-energy emission from the radio lobes

Modelling of the spectral energy distribution of Fornax A: leptonic and hadronic production of high-energy emission from the radio lobes

We present new low-frequency observations of the nearby radio galaxy Fornax A at 154 MHz with the Murchison Widefield Array, microwave flux-density measurements obtained from WMAP and Planck data, and γ-ray flux densities obtained from Fermi data. We also compile a comprehensive list of previously p...

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Bibliographic Details
Main Authors: McKinley, B., Yang, R., López-Caniego, M., Briggs, F., Hurley-Walker, N., Wayth, Randall, Offringa, A., Crocker, R., Bernardi, G., Procopio, P., Gaensler, B., Tingay, Steven, Johnston-Hollitt, M., McDonald, M., Bell, M., Bhat, N., Bowman, J., Cappallo, R., Corey, B., Deshpande, A., Emrich, D., Ewall-Wice, A., Feng, L., Goeke, R., Greenhill, L., Hazelton, B., Hewitt, J., Hindson, L., Jacobs, D., Kaplan, D., Kasper, J., Kratzenberg, E., Kudryavtseva, N., Lenc, E., Lonsdale, C., Lynch, M., McWhirter, S., Mitchell, D., Morales, M., Morgan, E., Oberoi, D., Ord, Stephen, Pindor, B., Prabu, T., Riding, J., Rogers, A., Roshi, D., Shankar, N., Srivani, K., Subrahmanyan, R., Waterson, M., Webster, R., Whitney, A., Williams, A., Williams, C.
Format: Journal Article
Published: OXFORD UNIV PRESS 2015
Online Access:http://hdl.handle.net/20.500.11937/38473
Description
Summary:We present new low-frequency observations of the nearby radio galaxy Fornax A at 154 MHz with the Murchison Widefield Array, microwave flux-density measurements obtained from WMAP and Planck data, and γ-ray flux densities obtained from Fermi data. We also compile a comprehensive list of previously published images and flux-density measurements at radio, microwave and X-ray energies. A detailed analysis of the spectrum of Fornax A between 154 and 1510 MHz reveals that both radio lobes have a similar spatially averaged spectral index, and that there exists a steep-spectrum bridge of diffuse emission between the lobes. Taking the spectral index of both lobes to be the same, we model the spectral energy distribution of Fornax A across an energy range spanning 18 orders of magnitude, to investigate the origin of the X-ray and γ-ray emission. A standard leptonic model for the production of both the X-rays and γ-rays by inverse-Compton scattering does not fit the multiwavelength observations. Our results best support a scenario where the X-rays are produced by inverse-Compton scattering and the γ-rays are produced primarily by hadronic processes confined to the filamentary structures of the Fornax A lobes.

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