New ALMA and Fermi/LAT Observations of the large-scale jet of PKS
  0637-752 Strengthen the Case Against the IC/CMB Model
  The Chandra X-ray observatory has discovered several dozen anomalously
X-ray-bright jets associated with powerful quasars. A popular explanation for
the X-ray flux from the knots in these jets is that relativistic
synchrotron-emitting electrons inverse-Compton scatter Cosmic Microwave
Background (CMB) photons to X-ray energies (the IC/CMB model). This model
predicts a high gamma-ray flux which should be detectable by the Fermi Large
Area Telescope (LAT) for many sources. GeV-band upper limits from Fermi/LAT for
the well-known anomalous X-ray jet in PKS 0637-752 were previously shown in
Meyer et al., (2015) to violate the predictions of the IC/CMB model.
Previously, measurements of the jet synchrotron spectrum, important for
accurately predicting the gamma-ray flux level, were lacking between radio and
infrared wavelengths. Here we present new Atacama Large
Millimeter/submillimeter Array (ALMA) observations of the large-scale jet at
100, 233, and 319 GHz which further constrain the synchrotron spectrum,
supporting the previously published empirical model. We also present updated
limits from the Fermi/LAT using the new `Pass 8' calibration and approximately
30% more time on source. With these deeper limits we rule out the IC/CMB model
at the 8.7 sigma level. Finally, we demonstrate that complete knowledge of the
synchrotron SED is critical in evaluating the IC/CMB model.
