X-Ray-to-Radio Offset Inference from Low-Count X-Ray Jets

TL;DR

This study detects positional offsets between X-ray and radio emissions in low-count extragalactic jets using a novel algorithm, challenging existing emission models and providing new insights into jet physics.

Contribution

Introduces the use of LIRA for analyzing low-count X-ray jets, enabling detection of offsets previously obscured in shallow observations.

Findings

55% of knots with offsets have X-ray peaks upstream of radio

Detected offsets challenge one-zone emission models

Non-detection of two previously claimed X-ray jets

Abstract

Observations of positional offsets between the location of X-ray and radio features in many resolved, extragalactic jets indicates that the emitting regions are not co-spatial, an important piece of evidence in the debate over the origin of the X-ray emission on kpc scales. The existing literature is nearly exclusively focused on jets with sufficiently deep Chandra observations to yield accurate positions for X-ray features, but most of the known X-ray jets are detected with tens of counts or fewer, making detailed morphological comparisons difficult. Here we report the detection of X-ray-to-radio positional offsets in 15 extragalactic jets from an analysis of 22 sources with low-count Chandra observations, where we utilized the Low-count Image Reconstruction Algorithm (LIRA). This algorithm has allowed us to account for effects such as Poisson background fluctuations and nearby point sources which have previously made the detection of offsets difficult in shallow observations. Using this method, we find that in 55 % of knots with detectable offsets, the X-rays peak upstream of the radio, questioning the applicability of one-zone models, including the IC/CMB model for explaining the X-ray emission. We also report the non-detection of two previously claimed X-ray jets. Many, but not all, of our sources, follow a loose trend of increasing offset between the X-ray and radio emission, as well as a decreasing X-ray to radio flux ratio along the jet.