Emission from Large-scale Jets in Quasars

TL;DR

This paper investigates the emission mechanisms in large-scale quasar jets, highlighting the presence of two spectral components and discussing how recent observations challenge previous models, emphasizing the role of synchrotron radiation.

Contribution

It provides new insights into the spectral components of quasar jets, favoring synchrotron origin for high-energy emission over inverse-Compton scattering, based on multi-wavelength data.

Findings

Identification of two distinct spectral components in quasar jets.

Recent data favor synchrotron radiation as the origin of high-energy emission.

Future observations will further constrain jet emission models.

Abstract

We consider the emission processes in the large-scale jets of powerful quasars based on the results obtained with the VLA, Spitzer, Hubble, and Chandra. We show that two well-known jets, 3C 273 and PKS 1136-135, have two distinct spectral components on large-scales: (1) the low-energy (LE) synchrotron spectrum extending from radio to infrared, and (2) the high-energy (HE) component arising from optical and extending to X-rays. The X-ray emission in quasar jets is often attributed to inverse-Compton scattering of cosmic microwave background (CMB) photons by radio-emitting electrons in a highly relativistic jet. However, recent data prefer synchrotron radiation by a second distinct population as the origin of the HE component. We anticipate that optical polarimetry with Hubble will establish the synchrotron nature of the HE component. Gamma-ray observations with GLAST (renamed as the Fermi Gamma-ray Space Telescope), as well as future TeV observations, are expected to place important constraints on the jet models.