The composite X-ray spectra of radio-loud and radio-quiet SDSS quasars

TL;DR

This study compares the X-ray and optical spectra of radio-loud and radio-quiet SDSS quasars, revealing higher X-ray emission in radio-loud quasars and correlations with radio loudness, supporting a corona-jet connection.

Contribution

It provides the first composite X-ray spectra comparison between radio-loud and radio-quiet SDSS quasars, highlighting the relationship with radio loudness and supporting the corona-jet model.

Findings

Radio-loud quasars have higher X-ray emission than radio-quiet quasars.

X-ray spectra increase with radio loudness.

Significant correlation between optical-to-X-ray index and radio loudness.

Abstract

We present the study on the X-ray emission for a sample of radio-detected quasars constructed from the cross-matches between SDSS, FIRST catalogs and XMM-Newton archives. A sample of radio-quiet SDSS quasars without FIRST radio detection is also assembled for comparison. We construct the optical and X-ray composite spectra normalized at rest frame $4215\,\rm \AA$ (or $2200\,\rm \AA$) for both radio-loud quasars (RLQs) and radio-quiet quasars (RQQs) at $z\le3.2$, with matched X-ray completeness of 19\%, redshift and optical luminosity. While the optical composite spectrum of RLQs is similar to that of RQQs, we find that RLQs have higher X-ray composite spectrum than RQQs, consistent with previous studies in the literature. By dividing the radio-detected quasars into radio loudness bins, we find the X-ray composite spectra are generally higher with increasing radio loudness. Moreover, a significant correlation is found between the optical-to-X-ray spectral index and radio loudness, and there is a unified multi-correlation between the radio, X-ray luminosities and radio loudness in radio-detected quasars. These results could be possibly explained with the corona-jet model, in which the corona and jet are directly related.