Hubble Space Telescope far-ultraviolet imaging of the jet in 3C273: a common emission component from optical to X-rays

TL;DR

This study uses Hubble Space Telescope far-ultraviolet imaging to reveal a common emission component in the jet of quasar 3C 273, linking UV and X-ray emissions and supporting a synchrotron origin hypothesis.

Contribution

It provides new UV observations showing a spectral upturn and a common UV/X-ray emission component in the jet, suggesting a synchrotron origin for X-ray emission.

Findings

UV flux upturn at 150 nm in the jet

UV flux compatible with X-ray power-law extrapolation

Supports a common origin of UV and X-ray emissions

Abstract

We present far-ultraviolet (UV) observations at 150 nm of the jet of the quasar 3C 273 obtained with the Advanced Camera for Survey's Solar Blind Channel (ACS/SBC) on board the Hubble Space Telescope. While the jet morphology is very similar to that in the optical and near-ultraviolet, the spectral energy distributions (SEDs) of the jet's sub-regions show an upturn in nu f_nu at 150 nm compared to 300 nm everywhere in the jet. Moreover, the 150 nm flux is compatible with extrapolating the X-ray power-law down to the ultra-violet region. This constitutes strong support for a common origin of the jet's far-UV and X-ray emission. It implies that even a substantial fraction of the *visible light* in the X-ray brightest parts of the jet arises from the same spectral component as the X-rays, as had been suggested earlier based on Spitzer Space Telescope observations. We argue that the identification of this UV/X-ray component opens up the possibility to establish the synchrotron origin of the X-ray emission by optical polarimetry.