Fermi non-detections of four X-ray jet sources and implications for the
  IC/CMB mechanism
  Since its launch in 1999, the Chandra X-ray observatory has discovered
several dozen X-ray jets associated with powerful quasars. In many cases the
X-ray spectrum is hard and appears to come from a second spectral component.
The most popular explanation for the kpc-scale X-ray emission in these cases
has been inverse-Compton (IC) scattering of Cosmic Microwave Background (CMB)
photons by relativistic electrons in the jet (the IC/CMB model). Requiring the
IC/CMB emission to reproduce the observed X-ray flux density inevitably
predicts a high level of gamma-ray emission which should be detectable with the
Fermi Large Area Telescope (LAT). In previous work, we found that gamma-ray
upper limits from the large scale jets of 3C 273 and PKS 0637-752 violate the
predictions of the IC/CMB model. Here we present Fermi/LAT flux density upper
limits for the X-ray jets of four additional sources: PKS 1136-135, PKS
1229-021, PKS 1354+195, and PKS 2209+080, and show that these limits violate
the IC/CMB predictions at a very high significance level. We also present new
Hubble Space Telescope (HST) observations of the quasar PKS 2209+080 showing a
newly detected optical jet, and Atacama Large Millimeter/submillimeter Array
(ALMA) band 3 and 6 observations of all four sources, which provide key
constraints on the spectral shape that enable us to rule out the IC/CMB model.
