The Origin of the X-ray Emission in Two Well-Aligned Extragalactic Jets: The Case for IC/CMB

TL;DR

This study provides evidence supporting the IC/CMB model for X-ray emission in two quasar jets by detecting gamma-ray flux levels consistent with predictions, challenging the alternative synchrotron explanation.

Contribution

The paper reports the first detection of gamma-ray flux levels consistent with the IC/CMB model in two well-aligned quasar jets, supporting the model's validity.

Findings

Gamma-ray flux levels match IC/CMB predictions in both sources.

Both jets exhibit extreme superluminal motions.

Long-term Fermi/LAT monitoring could confirm non-variable emission.

Abstract

Over the past two decades, the most commonly adopted explanation for high and hard X-ray emission in resolved quasar jets has been inverse Compton upscattering of the Cosmic Microwave Background (IC/CMB), which requires jets which remain highly relativistic on 10-1000 kpc scales. In more recent years various lines of observational evidence, including gamma-ray upper limits, have disfavored this explanation in favor of a synchrotron origin. While the IC/CMB model generally predicts a high level of gamma-ray emission, it has never been detected. Here we report the detection of a low-state Fermi/LAT gamma-ray spectrum associated with two jetted AGN which is consistent with the predictions of the IC/CMB model for their X-ray emission. We have used archival multiwavelength observations to make precise predictions for the expected minimum flux in the GeV band, assuming that the X-ray emission from the kpc-scale jet is entirely due to the IC/CMB process. In both sources -- OJ 287 and PKS 1510-089 -- the minimum-detected gamma-ray flux level agrees with predictions. Both sources exhibit extreme superluminal proper motions relative to their jet power, which argues for the well-aligned jets required by the IC/CMB model. In the case of PKS~1510-089, it cannot be ruled out that the minimum gamma-ray flux level is due to a low state of the variable core which only matches the IC/CMB prediction by chance. Continued long-term monitoring with the Fermi/LAT could settle this issue by detecting a plateau signature in the recombined light-curve which would clearly signal the presence of a non-variable emission component.