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The X-ray emission mechanism of powerful extragalactic jets—which has important implications for their environmental impacts—is poorly understood. The X-ray/radio positional offsets in the individual features of jets provide important clues. Extending previous work in Reddy et al., we present a detailed comparison between X-ray maps, deconvolved using the Low-count Image Reconstruction and Analysis tool, and radio maps of 164 components from 77 Chandra-detected X-ray jets. We detect 94 offsets (57%), with 58 new detections. In FR II–type jet knots, the X-rays peak and decay before the radio in about half the cases, disagreeing with the predictions of one-zone models. While a similar number of knots lack statistically significant offsets, we argue that projection and distance effects result in offsets below the detection level. Similar deprojected offsets imply that X-rays could be more compact than radio for most knots, and we qualitatively reproduce this finding with a “moving-knot” model. The bulk Lorentz factor (Γ) derived for knots under this model is consistent with previous radio-based estimates, suggesting that kiloparsec-scale jets are only mildly relativistic. An analysis of the X-ray/radio flux ratio distributions does not support the commonly invoked mechanism of X-ray production from inverse Compton scattering of the cosmic microwave background, but does show a marginally significant trend of declining flux ratio as a function of the distance from the core. Our results imply the need for multi-zone models to explain the X-ray emission from powerful jets. We provide an interactive list of our X-ray jet sample athttp://astro.umbc.edu/Atlas-X.

Over ∼150 resolved, kpc-scale X-ray jets hosted by active galactic nuclei have been discovered with the Chandra X-ray Observatory. A significant fraction of these jets have an X-ray spectrum either too high in flux or too hard to be consistent with the high-energy extension of the radio-to-optical synchrotron spectrum, a subtype we identify as Multiple Spectral Component (MSC) X-ray jets. A leading hypothesis for the origin of the X-rays is the inverse-Compton scattering of the cosmic microwave background by the same electron population producing the radio-to-optical synchrotron spectrum (known as the IC/CMB model). In this work, we test the IC/CMB model in 45 extragalactic X-ray jets using observations from the Fermi Large Area Telescope to look for the expected high level of gamma-ray emission, utilizing observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Hubble Space Telescope (HST) when possible to best constrain the predicted gamma-ray flux. Including this and previous works, we now find the IC/CMB model to be ruled out in a total of 24/45 MSC X-ray jets due to its over-prediction for the observed MeV-to-GeV gamma-ray flux. We present additional evidence against the IC/CMB model, including the relative X-ray-to-radio relativistic beaming in these sources, and the general mismatch between radio and X-ray spectral indexes. Finally, we present upper limits on the large-scale bulk-flow Lorentz factors for all jets based on the Fermi upper limits, which suggest that these jets are at most mildly relativistic.