Modelling of the Spectral Energy Distribution of Fornax A : Leptonic and Hadronic Production of High Energy Emission from the Radio Lobes
View/
Author
McKinley, B.
Yang, R.
López-Caniego, M.
Briggs, F.
Hurley-Walker, N.
Wayth, R. B.
Offringa, A. R.
Crocker, R.
Bernardi, G.
Procopio, P.
Gaensler, B. M.
Tingay, S. J.
Johnston-Hollitt, M.
McDonald, M.
Bell, M.
Bhat, N. D. R.
Bowman, J. D.
Cappallo, R. J.
Corey, B. E.
Deshpande, A. A.
Emrich, D.
Ewall-Wice, A.
Feng, L.
Goeke, R.
Greenhill, L. J.
Hazelton, B. J.
Hewitt, J. N.
Hindson, L.
Jacobs, D.
Kaplan, D. L.
Kasper, J. C.
Kratzenberg, E.
Kudryavtseva, N.
Lenc, E.
Lonsdale, C. J.
Lynch, M. J.
McWhirter, S. R.
Mitchell, D. A.
Morales, M. F.
Morgan, E.
Oberoi, D.
Ord, S. M.
Pindor, B.
Prabu, T.
Riding, J.
Rogers, A. E. E.
Roshi, D. A.
Shankar, N. Udaya
Srivani, K. S.
Subrahmanyan, R.
Waterson, M.
Webster, R. L.
Whitney, A. R.
Williams, A.
Williams, C. L.
Attention
2299/18999
Abstract
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 gamma-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 MHz 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 eighteen orders of magnitude, to investigate the origin of the X-ray and gamma-ray emission. A standard leptonic model for the production of both the X-rays and gamma-rays by inverse-Compton scattering does not fit the multi-wavelength observations. Our results best support a scenario where the X-rays are produced by inverse-Compton scattering and the gamma-rays are produced primarily by hadronic processes confined to the filamentary structures of the Fornax A lobes.