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

B. McKinley*, R. Yang, M. López-Caniego, F. Briggs, N. Hurley-Walker, R. B. Wayth, A. R. Offringa, R. Crocker, G. Bernardi, P. Procopio, B. M. Gaensler, S. J. Tingay, M. Johnston-Hollitt, M. McDonald, M. Bell, N. D.R. Bhat, J. D. Bowman, R. J. Cappallo, B. E. Corey, A. A. DeshpandeD. Emrich, A. Ewall-Wice, L. Feng, R. Goeke, L. J. Greenhill, B. J. Hazelton, J. N. Hewitt, L. Hindson, D. Jacobs, D. L. Kaplan, J. C. Kasper, E. Kratzenberg, N. Kudryavtseva, E. Lenc, C. J. Lonsdale, M. J. Lynch, S. R. McWhirter, D. A. Mitchell, M. F. Morales, E. Morgan, D. Oberoi, S. M. Ord, B. Pindor, T. Prabu, J. Riding, A. E.E. Rogers, D. A. Roshi, N. Udaya Shankar, K. S. Srivani, R. Subrahmanyan, M. Waterson, R. L. Webster, A. R. Whitney, A. Williams, C. L. Williams

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    43 Citations (Scopus)


    We present new low-frequency observations of the nearby radio galaxy Fornax A at 154MHz 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 1510MHz 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.

    Original languageEnglish
    Pages (from-to)3478-3491
    Number of pages14
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number4
    Publication statusPublished - 1 Feb 2015


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