On the origin of radio emission in radio-quiet quasars

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 ∼103 times weaker, and its origin is not established yet. We show here that there is a strong correlation between the radio luminosity (LR) and X‐ray luminosity (LX) with LR∼ 10−5LX, 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 active galactic nuclei (AGN). A remarkably similar correlation, known as the Güdel–Benz relation, where LR/LX∼ 10−5, holds for coronally active stars. The Güdel–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 ultraluminous X‐ray sources and Galactic black holes may be of coronal origin as well.

On the role of magnetic reconnection in jet/accretion disk systems

“…The diagram of the magnetic energy rate released by violent reconnection as a function of the black hole (BH) mass spanning 10 9 orders of magnitude (Figure 1) shows that the magnetic reconnection power is more than sufficient to explain the observed radio luminosities of the outbursts, from microquasars to low luminous AGNs (LINERs and Seyfert galaxies). This result is consistent with recently found empirical relation that correlates the observed radio emission from microquasars and radio quiet AGNs to that of magnetically active stars (Laor & Behar 2008;Soker & Vrtilek 2009), suggesting that it is mainly due to magnetic activity in the coronae and therefore, is nearly independent of 248 E. M. de Gouveia dal Pino et al the intrinsic physics of the central source and the accretion disk. The correlation found in Figure 1 does not hold for radio-loud AGNs, possibly because their surroundings are much denser and then "mask" the emission due to coronal magnetic activity.…”

Discovery of millimetre-wave excess emission in radio-quiet active galactic nuclei

“…However, the possible contamination from unresolved radio jets cannot be ruled out. The physical size in pc of an opaque (self-absorbed) synchrotron source can be estimated from the measured flux (e.g., Laor & Behar 2008) to be:…”

“…This suggests that radio emission from RQ AGN is due to magnetic coronal activity, akin to that of stellar coronae. Since the LR/LX ∼ 10 −5 relation is accepted as a manifestation of coronal heating by energetic electrons following magnetic reconnection in cool-stars, which subsequently gives rise to X-ray emission, the correlation presented in Laor & Behar (2008) over 20 orders of magnitude in luminosity raises the possibility that radio emission in RQ AGN may also be related to coronal, magnetic activity.…”

“…Laor & Behar (2008) used the PG quasar sample (Schmidt & Green 1983) to demonstrate that not only are LR(≡ νLν at 5 GHz) and LX (0.2 -20 keV) correlated over a large range of AGN luminosity, but that the correlation follows the well established relation for coronally active cool stars LR/LX ∼ 10 −5 (Güdel & Benz 1993). This suggests that radio emission from RQ AGN is due to magnetic coronal activity, akin to that of stellar coronae.…”

Discovery of five low-luminosity active galactic nuclei at the centre of the Perseus cluster

“…The columns are the following: source name, 1.4 GHz flux density from WSRT (Sijbring 1993), 1.4 GHz flux density ratio of EVN (our observation) and WSRT (Sijbring 1993), implied star formation rates per unit area from our EVN observation, the total star formation rates derived from the radio (EVN), FIR, Hα, and X-ray luminosities, and the X-ray luminosity measured by Chandra (Santra et al 2007 NGC 1277, 9 × 10 −3 for NGC 1278, and 7 × 10 −3 for VZw 339. They are at least one order higher than the Güdel-Benz relation, L R /L X ∼ 10 −5 , which is observed by Laor & Behar (2008) for the radio-quiet Palomar-Green quasar sample and where L R is the radio luminosity at 5 GHz and L X is the bolometric 0.2 -20 keV X-ray luminosity. Together with their high brightness temperature and the absence of large variability, we are in favour of synchrotron emission from compact jets rather than free-free emission from accretion disk winds (e.g.…”