The central engines of radio-quiet quasars

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 05/1998; DOI: 10.1046/j.1365-8711.1998.01752.x
Source: arXiv

ABSTRACT Two rival hypotheses have been proposed for the origin of the compact radio flux observed in radio-quiet quasars (RQQs). It has been suggested that the radio emission in these objects, typically some two or three orders of magnitude less powerful than in radio-loud quasars (RLQs), represents either emission from a circumnuclear starburst or is produced by radio jets with bulk kinetic powers 10^3 times lower than those of RLQs with similar luminosity ratios in other wavebands. We describe the results of high resolution (parsec-scale) radio-imaging observations of a sample of 12 RQQs using the Very Long Baseline Array (VLBA). We find strong evidence for jet-producing central engines in 8 members of our sample. Comment: 7 pages, 8 figures. Accepted for publication in MNRAS

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    ABSTRACT: We present a model for the radio emission from radio-quiet quasar nuclei. We show that a thermal origin for the high brightness temperature, flat spectrum point sources (known as radio ``cores'') is possible provided that the emitting region is hot and optically thin. We hence demonstrate that optically thin bremsstrahlung from a slow, dense disk wind can make a significant contribution to the observed levels of radio core emission. This is a much more satisfactory explanation, particularly for sources where there is no evidence of a jet, than a sequence of self-absorbed synchrotron components that collectively conspire to give a flat spectrum. Furthermore, such core phenomena are already observed directly via milliarcsecond radio imaging of the Galactic microquasar SS 433 and the active galaxy NGC 1068. We contend that radio-emitting disk winds must be operating at some level in radio-loud quasars and radio galaxies as well (although in these cases, observations of the radio cores are frequently contaminated/dominated by synchrotron emission from jet knots). This interpretation of radio core emission mandates mass accretion rates that are substantially higher than Eddington. Moreover, acknowledgment of this mass-loss mechanism as an AGN feedback process has important implications for the input of energy and hot gas into the intergalactic medium (IGM) since it is considerably less directional than that from jets.
    The Astrophysical Journal 01/2007; 668(2). · 6.73 Impact Factor
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    ABSTRACT: We present the results of a comparative study of the intra-night optical variability (INOV) characteristics of radio-loud and radio-quiet quasars, which involves a systematic intra-night optical monitoring of seven sets of high luminosity AGNs covering the redshift range {\it z} $\simeq 0.2$ to {\it z} $\simeq 2.2$. The sample, matched in the optical luminosity -- redshift (M$_B$ -- z) plane, consists of seven radio-quiet quasars (RQQs), eight radio lobe-dominated quasars (LDQs), six radio core-dominated quasars (CDQs) and five BL Lac objects (BLs). Systematic CCD observations, aided by a careful data analysis procedure, have allowed us to detect INOV with amplitudes as low as 1%. Present observations cover a total of 113 nights (720 hours) with only a single quasar monitored as continuously as possible on a night. Considering cases of only unambiguous detections of INOV we have estimated duty cycles (DCs) of 17%, 12%, 20% and 72% respectively for RQQs, LDQs, CDQs, and BLs. The low amplitude and low DC of INOV shown by RQQs compared to BLs can be understood in terms of their having optical synchrotron jets which are modestly misdirected from us. From our fairly extensive dataset, no unambiguous general trend of a correlation between the INOV amplitude and the apparent optical brightness of the quasar is noticed. Comment: 36 pages, 14 Figures, due to large size Fig. 5,6,11 and 12 are not included. Intersted people contact to Submitted to Journal of Astrophysics and Astronomy
    Journal of Astrophysics and Astronomy 06/2003; · 0.34 Impact Factor
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    ABSTRACT: The differences among apparently diverse classes of AGN are mainly the result of viewing the central engine at different orientations, because dust, which absorbs and scatters the light, partially covers the central source, and because synchrotron emission is highly beamed along the relativistic jet. Also important are factors independent of orientation: the total power output, the unknown mover behind the eigenvector 1 relationships, and the radio-loudness. These other factors may not be independent of the parameters of Unified models, such as intrinsic jet physics, AGN dust content, and torus thickness. We outline the basic evidence for orientation Unified Schemes, and briefly discuss their importance for understanding the mechanisms of the central engine and its relation to the surrounding host galaxy and beyond.


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