It has been proposed that the radio spectra of radio-quiet quasars is produced by free-free emission in the optically thin part of an accretion disc wind. An important observational constraint on this model is the observed X-ray luminosity. We investigate this constraint using a sample of PG radio-quiet quasars for which XMM-Newton EPIC spectra are available. Comparing the predicted and measured luminosities for 0.5, 2 and 5 keV, we conclude that all of the studied PG quasars require a large hydrogen column density absorber, requiring these quasars to be close to or Compton-thick. Such a large column density can be directly excluded for PG 0050+124, for which a high-resolution RGS spectrum exists. Further constraint on the column density for a further 19 out of the 21 studied PG quasars comes from the EPIC spectrum characteristics such as hard X-ray power-law photon index and the equivalent width of the Fe Kalpha line; and the small equivalent width of the C IV absorber present in UV spectra. For 2 sources: PG 1001+054 and PG 1411+442 we cannot exclude that they are indeed Compton-thick, and the radio and X-ray luminosity are due to a wind originating close to the super-massive black hole. We conclude that for 20 out of 22 PG quasars studied free-free emission from a wind emanating from the accretion disc cannot mutually explain the observed radio and X-ray luminosity.
Based on a recently started programme, we report the first search for intranight optical variability among radio-quiet weak-line-quasars (RQWLQs). Eight members of this class were observed on 13 nights in the R-band, such that each source was monitored continuously at least once for a minimum duration of about 3.5 hours, using the recently installed 130 cm telescope at Devasthal, India. Statistical analysis of the differential light curves was carried out using two versions of the F-test. Based on the INOV data acquired so far, the radio-quiet WLQ population appears to exhibit stronger INOV ac…
Fifty-nine quasars in the background of the Magellanic Clouds had brightness records monitored by the MACHO project during the years 1992 - 99. Because the circumpolar fields of these quasars had no seasonal sampling defects, their observation produced data sets well suited to further careful analysis. Following a preliminary report wherein we showed the existence of reverberation in the data for one of the radio-quiet quasars in this group, we now show that similar reverberations have been seen in all of the 55 radio-quiet quasars with adequate data, making possible the determination of the q…
We obtained SDSS spectra for a set of 37 radio-quiet quasars (RQQSOs) that had been previously examined for rapid small scale optical variations, or microvariability. Their H-beta and Mg II emission lines were carefully fit to determine line widths (FWHM) as well as equivalent widths (EW) due to the broad emission line components. The line widths were used to estimate black hole masses and Eddington ratios, ell. Both EW and FWHM are anticorrelated with ell. The EW distributions provide no evidence for the hypothesis that a weak jet component in the RQQSOs is responsible for their microvariabil…
We present 1-2 GHz Very Large Array A-configuration continuum observations on the highest redshift quasar known to date, the $z=7.085$ quasar ULAS J112001.48+064124.3. The results show no radio continuum emission at the optical position of the quasar or its vicinity at a level of $\geq 3σ$ or $23.1 μ$Jy beam$^{-1}$. This $3σ$ limit corresponds to a rest frame 1.4 GHz luminosity density limit of $L_{ν,1.4\,GHz} < 1.76 \times 10^{24}$ W Hz$^{-1}$ for a spectral index of $α=0$, and $L_{ν,1.4\,GHz} < 1.42 \times 10^{25}$ W Hz$^{-1}$ for a spectral index of $α=-1$. The rest-frame 1.4 GHz luminosity…
We present radio and X-ray observations, as well as optical light curves, for a subset of 26 BL Lac candidates from the Sloan Digital Sky Survey (SDSS) lacking strong radio emission and with z<2.2. Half of these 26 objects are shown to be stars, galaxies, or absorbed quasars. We conclude that the other 13 objects are Active Galactic Nuclei (AGN) with abnormally weak emission features; ten of those 13 are definitively radio-quiet, and, for those with available optical light curves, their level of optical flux variability is consistent with radio-quiet quasars. We cannot exclude the possibility …
In the restframe UV, two of the parameters that best characterize the range of emission-line properties in quasar broad emission-line regions are the equivalent width and the blueshift of the CIV line relative to the quasar rest frame. We explore the connection between these emission-line properties and the UV through X-ray spectral energy distribution (SED) for radio-quiet (RQ) quasars. Our sample consists of a heterogeneous compilation of 406 quasars from the Sloan Digital Sky Survey and Palomar-Green survey that have well-measured CIV emission-line and X-ray properties (including 164 object…
There are several lines of evidence that active galactic nuclei (AGN) can be regarded as scaled-up X-ray binaries (XRB). The timescales of the evolutionary phenomena in these two classes are proportional to the black hole (BH) masses. Consequently, unlike in the case of XRBs, the evolution of AGNs is too slow to be followed directly. What could be done, however, is to assign particular types of active galaxies to different evolutionary stages observable in XRBs. We studied such an assignment for three quasars with clear signatures of a recent transition from the radio-loud to the radio-quiet s…
In the context of AGN unification scheme rapid variability properties play an important role in understanding any intrinsic differences between sources in different classes. In this respect any clue based on spectral properties will be very useful toward understanding the mechanisms responsible for the origin of rapid small scale optical variations, or microvariability. Here we have added spectra of 46 radio-quiet quasars (RQQSOs) and Seyfert 1 galaxies to those of our previous sample of 37 such objects, all of which had been previously searched for microvariability. We took new optical spectr…
The dichotomy between radio-loud and radio-quiet QSOs is not simply one of host morphology. While spiral galaxies almost exclusively host radio-quiet QSOs, ellipticals can host either radio-louds or radio-quiets. We find that a combination of accretion rate and host scale determines which type of QSO a given elliptical galaxy will host. QSOs with high x-ray luminosities (above 10^44.5 erg/s at 0.5 keV) are mostly radio-loud. But those with low luminosities divide fairly neatly in size (measured by the half-light radius, r_e). Those larger than about 10 kpc are radio-loud, while smaller ones ar…
The prevalence and energetics of quasar feedback is a major unresolved problem in galaxy formation theory. In this paper, we present Gemini Integral Field Unit observations of ionized gas around eleven luminous, obscured, radio-quiet quasars at z~0.5 out to ~15 kpc from the quasar; specifically, we measure the kinematics and morphology of [O III]5007 emission. The round morphologies of the nebulae and the large line-of-sight velocity widths (with velocities containing 80% of the emission as high as 1000 km/s combined with relatively small velocity difference across them (from 90 to 520 km/s) p…
We examine the fundamental plane of black hole activity for correlations with redshift and radio loudness in both radio-loud and radio-quiet quasar populations. Sources are compiled from archival data of both radio-loud and radio-quiet quasars over redshifts $0.1 < z < 5.0$ to produce a sample of 353 sources with known X-ray, radio, and black hole mass measurements. A fundamental plane of accretion activity is fit to a sample of radio-loud and radio-quiet quasars, and we find a dichotomy between radio-loud and radio-quiet sources. The set of best-fit equations that best describe the two sample…
We conduct kinematic analysis of the SDSS spectra of 568 obscured luminous quasars, with the emphasis on the kinematic structure of the [OIII]5007 emission line. [OIII] emission tends to show blueshifts and blue excess, which indicates that at least part of the narrow-line gas is undergoing an organized outflow. The velocity width containing 90% of line power ranges from 370 to 4780 km/sec, suggesting outflow velocities up to 2000 km/sec. The velocity width of the [OIII] emission is positively correlated with the radio luminosity among the radio-quiet quasars. We propose that radio emission in…
Black hole feedback -- the strong interaction between the energy output of supermassive black holes and their surrounding environments -- is routinely invoked to explain the absence of overly luminous galaxies, the black hole vs. bulge correlations and the similarity of black hole accretion and star formation histories. Yet direct probes of this process in action are scarce and limited to small samples of active nuclei. We present Gemini IFU observations of the distribution of ionized gas around luminous, obscured, radio-quiet (RQ) quasars at z~0.5. We detect extended ionized gas nebulae via […
This is continuation of our programme to search for the elusive radio-quiet BL Lacs, by carrying out a systematic search for intranight optical variability (INOV) in a subset of `weak-line quasars' which are already designated as `high-confidence BL Lac candidate' and are also known to be radio-quiet. For 6 such radio-quiet weak-line quasars (RQWLQs), we present here new INOV observations taken in 11 sessions of duration >3 hours each. Combining these data with our previously published INOV monitoring of RQWLQs in 19 sessions yields INOV observations for a set of 15 RQWLQs monitored in 30 sess…
(Abriged) Intranight polarization variability in AGN has not been studied extensively so far. Studying the variability in polarization makes it possibly to distinguish between different emission mechanisms. Thus it can help answering the question if intranight variability in radio-loud and radio-quiet AGN is of the same or of fundamentally different origin. In this paper we investigate intranight polarization variability in AGN. Our sample consists of 28 AGN at low to moderate redshifts (0.048 < z < 1.036), 12 of which are radio-quiet quasars (RQQs) and 16 are radio-loud blazars. The subsample…
We present e-MERLIN and EVN observations which reveal unambiguous jet activity within radio quiet quasar HS~0810+2554. With an intrinsic flux density of 880~nJy, this is the faintest radio source ever imaged. The findings present new evidence against the idea that radio loud and radio quiet quasars are powered by different underlying radio emission mechanisms, showing instead that the same AGN mechanism can operate as the dominant source of radio emission even in the very lowest radio luminosity quasars. Thanks to strong gravitational lensing, our source is not only visible, but with VLBI is i…
We report the results from Chandra and XMM-Newton observations of a sample of 10 type 1 quasars selected to have unusual UV emission-line properties (weak and blueshifted high-ionization lines; strong UV Fe emission) similar to those of PHL 1811, a confirmed intrinsically X-ray weak quasar. These quasars were identified by the Sloan Digital Sky Survey at high redshift (z~2.2); eight are radio quiet while two are radio intermediate. All of the radio-quiet PHL 1811 analogs are notably X-ray weak by a mean factor of ~13. These sources lack broad absorption lines and have blue UV/optical continua,…
We present long-slit spectroscopic data which reveals extended Lyman alpha emission around the z=6.417 radio-quiet quasar CFHQS J2329-0301. The Lyman alpha emission is extended over 15 kpc and has a luminosity of > 8 x 10^36 W, comparable to the most luminous Lyman alpha halos known. The emission has complex kinematics, in part due to foreground absorption which only partly covers the extended nebula. The velocity ranges from -500 km/s to +500 km/s, with a peak remarkably close to the systemic velocity identified by broad MgII emission of the quasar. There is no evidence for infall or outflow …
We present near-infrared imaging obtained with ESO VLT/ISAAC of a sample of 16 low luminosity radio-quiet quasars at the epoch around the peak of the quasar activity (2 < z < 3), aimed at investigating their host galaxies. For 11 quasars, we are able to detect the host galaxies and derive their properties, while for the other five quasars, upper limits to the host luminosity are estimated. The luminosities of the host galaxies of radio-quiet quasars at high redshift are in the range of those of massive inactive elliptical galaxies. This work complements our previous systematic study of quasar …
Bolometric corrections are used in quasar studies to quantify total energy output based on a measurement of a monochromatic luminosity. First, we enumerate and discuss the practical difficulties of determining such corrections, then we present bolometric luminosities between 1 μm and 8 keV rest frame and corrections derived from the detailed spectral energy distributions of 63 bright quasars of low to moderate redshift (z = 0.03-1.4). Exploring several mathematical fittings, we provide practical bolometric corrections of the forms L_iso=ζλL_λ and log(L_iso)=A+B log(λL_λ) for λ= 1450, 3000, and…
We present VLA detections of radio emission in four four-image gravitational lens systems with quasar sources: HS0810+2554, RXJ0911+0511, HE0435$-$1223 and SDSSJ0924+0219, and e-MERLIN observations of two of the systems. The first three are detected at a high level of significance, and SDSS J0924+0219 is detected. HS0810+2554 is resolved, allowing us for the first time to achieve 10-mas resolution of the source frame in the structure of a radio quiet quasar. The others are unresolved or marginally resolved. All four objects are among the faintest radio sources yet detected, with intrinsic flux…
We analyze 1598 serendipitous Chandra X-ray observations of 462 radio-quiet quasars to constrain the frequency of extreme amplitude X-ray variability that is intrinsic to the quasar corona and innermost accretion flow. The quasars in this investigation are all spectroscopically confirmed, optically bright ($m_i \leq$ 20.2), and contain no identifiable broad absorption lines in their optical/ultraviolet spectra. This sample includes quasars spanning $z \approx$ 0.1 - 4 and probes X-ray variability on timescales of up to $\approx$ 12 rest-frame years. Variability amplitudes are computed between …
We have obtained IRTF/SpeX spectra of eight moderate-redshift (z=0.7-2.4), radio-selected (log R*~0.4-1.9) broad absorption line (BAL) quasars. The spectra cover the rest-frame optical band. We compare the optical properties of these quasars to those of canonically radio-quiet (log R*<1) BAL quasars at similar redshifts and to low-redshift quasars from the Palomar-Green catalog. As with previous studies of BAL quasars, we find that [OIII] 5007 is weak, and optical FeII emission is strong, a rare combination in canonically radio-loud (log R*>1) quasars. With our measurements of the optical prop…
The velocities of the [O III] 5007 and optical Fe II emission lines, measured relative to the systemic redshifts of 2265 QSOs by Hu et al. (2008), show the signature of a disklike BLR structure with polar outflows. Objects with large [O III] outflows show no Fe II offset velocity and are seen pole-on. Objects with large Fe II inflow show no [O III] offset velocity and are seen edge-on. This interpretation is supported by the morphology of the radio-loud objects within the sample and by previous determinations of the geometry of the broad and narrow line regions. Analysis of the objects with ne…
We present multi-frequency (1-8 GHz) VLA data, combined with VIMOS IFU data and HST imaging, of a z=0.085 radio-quiet type 2 quasar (with L(1.4GHz)~5e23 W/Hz and L(AGN)~2e45 erg/s). Due to the morphology of its emission-line region, the target (J1430+1339) has been referred to as the Teacup AGN in the literature. We identify "bubbles" of radio emission that are extended ~10-12 kpc to both the east and west of the nucleus. The edge of the brighter eastern bubble is co-spatial with an arc of luminous ionized gas. We also show that the Teacup AGN hosts a compact radio structure, located ~0.8 kpc …
We present the results of a comparison between the environments of 1) a complete sample of 46 southern 2Jy radio galaxies at intermediate redshifts (0.05 < z < 0.7), 2) a complete sample of 20 radio-quiet type-2 quasars (0.3 < z < 0.41), and 3) a control sample of 107 quiescent early-type galaxies at 0.2 < z < 0.7 in the Extended Groth Strip (EGS). The environments have been quantified using angular clustering amplitudes (Bgq) derived from deep optical imaging data. Based on these comparisons, we discuss the role of the environment in the triggering of powerful radio-loud and radio-quiet quasa…
In this Letter, the Evans and Koratkar Atlas of Hubble Space Telescope Faint Object Spectrograph Spectra of Active Galactic Nuclei and Quasars is used to study the redward asymmetry in CIV broad emission lines (BELs). It is concluded that there is a highly significant correlation between the spectral index from 10 GHz to 1350 $Å$ and the amount of excess luminosity in the red wing of the CIV BEL ($>99.9999%$ significance level for the full sample and the radio loud subsample independently, but no correlation is found for the radio quiet subsample). This is interpreted as a correlation between …
We report a dramatic fast X-ray dimming event in a z=2.627 radio-quiet type 1 quasar, which has an estimated supermassive black hole (SMBH) mass of $6.3\times 10^{9} M_\odot$. In the high X-ray state, it showed a typical level of X-ray emission relative to its UV/optical emission. Then its 0.5-2 keV (rest-frame 1.8-7.3 keV) flux dropped by a factor of $\approx7.6$ within two rest-frame days. The dimming is associated with spectral hardening, as the 2-7 keV (rest-frame 7.3-25.4 keV) flux dropped by only $17\%$ and the effective power-law photon index of the X-ray spectrum changed from $\approx2…
We report a candidate centi-parsec supermassive black hole binary (SMBHB) in the radio-quiet quasar SDSS J0159+0105 at z=0.217. With a modified lomb-scargle code GLSdeDRW and the auto-correlation analysis ACF, we detect two significant (at P>99%) periodic signals at ~741 day and ~1500 day from the 8.1-year Catalina V-band light curve of this quasar. The period ratio, which is close to 1:2, is typical of a black-hole binary system with a mass ratio of 0.05<q<0.8 according to recent numerical simulations. SDSS J0159+0105 has two SDSS spectroscopic observations separated by ~10 years. There is a …
We investigate the optical variability of 7658 quasars from SDSS Stripe 82. Taking advantage of a larger sample and relatively more data points for each quasar, we estimate variability amplitudes and divide the sample into small bins of redshift, rest-frame wavelength, black hole mass, Eddington ratio and bolometric luminosity respectively, to investigate the relationships between variability and these parameters. An anti-correlation between variability and rest-frame wavelength is found. The variability amplitude of radio-quiet quasars shows almost no cosmological evolution, but that of radio…
(Abridged) We report on the X-ray and multiwavelength properties of 11 radio-quiet quasars with weak or no emission lines identified by the Sloan Digital Sky Survey (SDSS) with redshift z=0.4-2.5. The distribution of relative X-ray brightness for our low-redshift weak-line quasar (WLQ) candidates is significantly different from that of typical radio-quiet quasars, having an excess of X-ray weak sources, but it is consistent with that of high-redshift WLQs. The X-ray weak sources generally show similar UV emission-line properties to those of the X-ray weak quasar PHL 1811; they may belong to th…
We present XMM-Newton imaging spectroscopy of ten weak emission-line quasars (WLQs) at $0.928\leq z \leq 3.767$, six of which are radio quiet and four which are radio intermediate. The new X-ray data enabled us to measure the power-law photon index, at rest-frame energies $>2$ keV, in each source with relatively high accuracy. These measurements allowed us to confirm previous reports that WLQs have steeper X-ray spectra, suggesting higher accretion rates with respect to 'typical' quasars. A comparison between the photon indices of our radio-quiet WLQs and those of a control sample of 85 source…
We present initial results from an exploratory X-ray monitoring project of two groups of comparably luminous radio-quiet quasars (RQQs). The first consists of four sources at 4.10 <= z <= 4.35, monitored by Chandra, and the second is a comparison sample of three sources at 1.33 <= z <= 2.74, monitored by Swift. Together with archival X-ray data, the total rest-frame temporal baseline spans ~2-4 yr and ~5-13 yr for the first and second group, respectively. Six of these sources show significant X-ray variability over rest-frame timescales of ~10^2 - 10^3 d; three of these also show significant X…
