A surprising excess of radio emission in extremely stable quasars: a unique clue to jet launching?

TL;DR

This study reveals an unexpected excess of radio emission in extremely stable quasars, suggesting a new connection between jet launching mechanisms and quasar stability, challenging previous assumptions about variability and radio loudness.

Contribution

It uncovers a significant excess of radio detection in extremely stable quasars, providing new insights into jet launching and the nature of radio emission in quasars.

Findings

Over 25% of ESQs are radio-detected, compared to 6-8% in control samples.

Radio detection in ESQs is significant at 4.4 sigma, mainly at intermediate radio loudness.

Radio detection fraction increases with more stringent stability thresholds.

Abstract

Quasars are generally divided into jetted radio-loud and non-jetted radio-quiet ones, but why only 10% quasars are radio loud has been puzzling for decades. Other than jet-induced-phenomena, black hole mass, or Eddington ratio, prominent difference between jetted and non-jetted quasars has scarcely been detected. Here we show a unique distinction between them and the mystery of jet launching could be disclosed by a prominent excess of radio emission in extremely stable quasars (ESQs, i.e., type 1 quasars with extremely weak variability in UV/optical over 10 years). Specifically, we find that $>$ 25% of the ESQs are detected by the FIRST/VLASS radio survey, while only $\sim$ 6-8% of the control sample, matched in redshift, luminosity, and Eddington ratio, are radio-detected. The excess of radio detection in ESQs has a significance of 4.4 $\sigma$ (99.9995%), and dominantly occurs at intermediate radio loudness with R $\sim$ 10 - 60. The radio detection fraction of ESQs also tends to increase in the ESQ samples selected with more stringent thresholds. Our results are in contrast to the common view that RL quasars are likely more variable in UV/optical due to jet contribution. New clues/challenge posed by our findings highlight the importance of extensive follow-up observations to probe the nature of jets in ESQs, and theoretical studies on the link between jet launching and ESQs. Moreover, our results makes ESQs, an essential population which has never been explored, unique targets in the burgeoning era of time domain astronomy, like their opposite counterparts of quasars exhibiting extreme variability or changing-look features.