The aox--HeII EW Connection in Radio-Loud Quasars

TL;DR

This study investigates the relationship between HeII equivalent width and $ m{ ext{ox}}$ in radio-loud quasars, revealing that some RLQs share emission mechanisms with radio-quiet quasars, while others exhibit jet-related X-ray excess.

Contribution

It demonstrates that steep-spectrum and low-luminosity flat-spectrum RLQs follow the same HeII EW--$ m{ ext{ox}}$ relation as RQQs, indicating similar EUV and X-ray emission mechanisms.

Findings

SSRQs and low-$L_{R}$ FSRQs follow the RQQ $ m{ ext{ox}}$--HeII EW relation.

High-$L_{R}$ FSRQs show X-ray excess by a factor of ~3.5.

X-ray emission in some RLQs is not jet-related, unlike in high-$L_{R}$ FSRQs.

Abstract

Radio-loud quasars (RLQs) are known to produce excess X-ray emission, compared to radio-quiet quasars (RQQs) of the same luminosity, commonly attributed to jet-related emission. Recently, we found that the HeII EW and $\alpha_{\rm{ox}}$ in RQQs are strongly correlated, which suggests that their extreme-ultraviolet (EUV) and X-ray emission mechanisms are tightly related. Using 48 RLQs, we show that steep-spectrum radio quasars (SSRQs) and low radio-luminosity ($L_{\rm R}$) flat-spectrum radio quasars (FSRQs) follow the $\alpha_{\rm ox}$--HeII EW relation of RQQs. This suggests that the X-ray and EUV emission mechanisms in these types of RLQs is the same as in RQQs, and is not jet related. High-$L_{\rm R}$ FSRQs show excess X-ray emission given their HeII EW by a factor of $\approx$ 3.5, which suggests that only in this type of RLQ is the X-ray production likely jet related.