Fermi Gamma-ray Space Telescope

Testing the IC/CMB model for the large scale jet X-ray emission in AGN with the Fermi/LAT

Peter Breiding
(Eileen T. Meyer, Markos Georganopoulos, Adursh Iyer, Mary Keenan, and Jennifer Hewitt)


The Chandra X-ray observatory has discovered kpc-scale X-ray jets in many powerful quasars over the past 2 decades (Harris & Krawczynski, 2006). In many cases these X-rays cannot be explained by the extension of the radio-optical spectrum produced by synchrotron-emitting electrons in the jet, since the observed X-ray flux is too high and/or the X-ray spectral index is too hard. A widely accepted model for the X-ray emission, first proposed by Celotti et al. (2001) and Tavecchio et al. (2000), posits that the X-rays are produced when relativistic electrons in the jet up-scatter ambient cosmic microwave background (CMB) photons via inverse-Compton scattering from microwave to X-ray energies (the IC/CMB model). However, modeling the X-ray emission in these jets with the IC/CMB model requires high levels of IC/CMB gamma-ray emission (Georganopoulos et al., 2006), which we have looked for using the Fermi/LAT gamma-ray space telescope. Another viable model for the large scale jet X-ray emission, favored by the results of Meyer et al. (2015) and Meyer & Georganopoulos (2014), is a second population of synchrotron-emitting electrons with up to multi-TeV energies. In contrast with the second synchrotron interpretation; the IC/CMB model requires jets with high kinetic powers (exceeding the Eddington luminosity in some cases), which remain highly relativistic (Γ~10) up to kpc scales. I will present recently obtained deep gamma-ray upper-limits from the Fermi/LAT which rule out the IC/CMB model in a large sample of sources previously modeled with IC/CMB, and discuss the properties of the growing sample of non-IC/CMB anomalous X-ray jets and the implications for jet energetics and environmental impact.