On the origin of radio emission in radio quiet quasars

TL;DR

This paper suggests that the radio emission in radio quiet quasars likely originates from magnetically heated coronae, similar to stellar coronae, based on a strong correlation between their radio and X-ray luminosities.

Contribution

It proposes a novel coronal origin for radio emission in RQQs, supported by a correlation analogous to the stellar Guedel-Benz relation, extending the understanding of AGN emission mechanisms.

Findings

Strong correlation between L_R and L_X in RQQs, with L_R~10^-5 L_X.

RQQs follow a similar L_R-L_X relation as stellar coronae, indicating a possible common magnetic heating process.

Implications for observing compact flat cores and correlated variability at GHz and hundreds of GHz frequencies.

Abstract

The radio emission in radio loud quasars originates in a jet carrying relativistic electrons. In radio quiet quasars (RQQs) the relative radio emission is ~10^3 times weaker, and its origin is not established yet. We show here that there is a strong correlation between the radio luminosity (L_R) and X-ray luminosity (L_X) with L_R~10^-5L_X, for the radio quiet Palomar-Green (PG) quasar sample. The sample is optically selected, with nearly complete radio and X-ray detections, and thus this correlation cannot be due to direct selection biases. The PG quasars lie on an extension of a similar correlation noted by Panessa et al., for a small sample of nearby low luminosity type 1 AGN. A remarkably similar correlation, known as the Guedel-Benz relation, where L_R/L_X~10^-5, holds for coronally active stars. The Guedel-Benz relation, together with correlated stellar X-ray and radio variability, implies that the coronae are magnetically heated. We therefore raise the possibility that AGN coronae are also magnetically heated, and that the radio emission in RQQ also originates in coronal activity. If correct, then RQQ should generally display compact flat cores at a few GHz due to synchrotron self-absorption, while at a few hundred GHz we should be able to see directly the X-ray emitting corona, and relatively rapid and large amplitude variability, correlated with the X-ray variability, is likely to be seen. We also discuss possible evidence that the radio and X-ray emission in ultra luminous X-ray sources and Galactic black holes may be of coronal origin as well.