An X-ray Imaging Survey of Quasar Jets -- Testing the Inverse Compton Model

TL;DR

This study uses Chandra X-ray observations of quasar jets to test the inverse Compton scattering model involving CMB photons, revealing complex dependencies on jet magnetic fields and possible jet deceleration.

Contribution

It provides the first extensive X-ray survey of quasar jets and critically tests the IC-CMB model against observational data, highlighting the need to consider jet deceleration.

Findings

X-ray detected in 24 of 39 jets observed

X-ray to radio flux ratios do not follow simple redshift dependence

Jet angles to line of sight are often smaller than IC-CMB model estimates

Abstract

We present results from continued Chandra X-ray imaging and spectroscopy of a flux-limited sample of flat spectrum radio-emitting quasars with jet-like extended structure. X-rays are detected from 24 of the 39 jets observed so far. We compute the distribution of alpha_rx, the spectral index between the X-ray and radio bands, showing that it is broad, extending at least from 0.8 to 1.2. While there is a general trend that the radio brightest jets are detected most often, it is clear that predicting the X-ray flux from the radio knot flux densities is risky so a shallow X-ray survey is the most effective means for finding jets that are X-ray bright. We test the model in which the X-rays result from inverse Compton (IC) scattering of cosmic microwave background (CMB) photons by relativistic electrons in the jet moving with high bulk Lorentz factor nearly along the line of sight. Depending on how the jet magnetic fields vary with z, the observed X-ray to radio flux ratios do not follow the redshift dependence expected from the IC-CMB model. For a subset of our sample with known superluminal motion based on VLBI observations, we estimate the angle of the kpc-scale jet to the line of sight by considering the additional information in the bends observed between pc- and kpc-scale jets. These angles are sometimes much smaller than estimates based on the IC-CMB model with a Lorentz factor of 15, indicating that these jets may decelerate significantly from pc scales to kpc scales.