A novel method for measuring the extragalactic background light: Fermi application to the lobes of Fornax A

Abstract

We describe a new method for measuring the extragalactic background light (EBL) through the detection of $\gamma$-ray inverse Compton (IC) emission due to scattering of the EBL photons off relativistic electrons in the lobes of radio galaxies. Our method has no free physical parameters and is a powerful tool when the lobes are characterized by a high energy sharp break or cutoff in their electron energy distribution (EED). We show that such a feature will produce a high energy IC `imprint' of the EBL spectrum in which the radio lobes are embedded, and show how this imprint can be used to derive the EBL. We apply our method to the bright nearby radio galaxy Fornax A, for which we demonstrate, using WMAP and EGRET observations, that the EED of its lobes is characterized by a conveniently located cutoff, bringing the IC EBL emission into the {\sl Fermi} energy range. We show that {\sl Fermi} will set upper limits to the optical EBL and measure the more elusive infrared EBL.

ApJL, accepted

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Cited by in corpus (24)

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• Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe
• Constraints on the Intergalactic Magnetic Field with Gamma-Ray Observations of Blazars
• Active galactic nuclei at gamma-ray energies
• Fermi Large Area Telescope Detection of Extended Gamma-Ray Emission from the Radio Galaxy Fornax A
• Limits on the extragalactic background light in the Fermi era
• Modelling of the Spectral Energy Distribution of Fornax A: Leptonic and Hadronic Production of High Energy Emission from the Radio Lobes
• Modeling the Extragalactic Background Light and the Cosmic Star Formation History
• A method for setting upper limits to the extragalactic background light with Fermi-LAT and TeV observations of blazars
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• Suzaku X-ray Imaging of the Extended Lobe in the Giant Radio Galaxy NGC6251 Associated with the Fermi-LAT Source 2FGLJ1629.4+8236
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• Wide and deep near-UV (360nm) galaxy counts and the extragalactic background light with the Large Binocular Camera
• A physical model for the origin of the diffuse cosmic infrared background
• Constraining Sources of Ultra High Energy Cosmic Rays Using High Energy Observations with the Fermi Satellite
• Gamma-ray emission in radio galaxies, from MeV to TeV