Related papers: Extending the Eigenvector 1 Space to the Optical V…
We present new Gemini/GMOS optical spectroscopy of 16 extreme variability quasars (EVQs) that dimmed by more than 1.5 mag in the $g$ band between the Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey (DES) epochs (separated by a…
Last year (2013) was more or less the 50th anniversary of the discovery of quasars. It is an interesting time to review what we know (and don't know) about them both empirically and theoretically. These compact sources involving line…
The 4D Eigenvector 1 parameter space was introduced seven years ago as an attempt at multiwavelength spectroscopic representation of quasars. It appears to be the most effective diagnostic space for unifying the diversity of broad line AGN.…
Context. X-ray spectral variability analyses of active galactic nuclei (AGN) with moderate luminosities and redshifts typically show a softer when brighter behaviour. Such a trend has rarely been investigated for high-luminosity AGNs ($…
Aims: Establish the dependence of variability properties, such as characteristic timescales and variability amplitude, on basic quasar parameters such as black hole mass and accretion rate, controlling for the rest-frame wavelength of…
We address the effect of orientation of the accretion disk plane and the geometry of the broad-line region (BLR) as part of an effort to understand the distribution of quasars in the optical plane of the quasar main sequence. We utilize the…
The enrichment of Fe, relative to alpha-elements such as O and Mg, represents a potential means to determine the age of quasars and probe the galaxy formation epoch. To explore how \ion{Fe}{2} emission in quasars is linked to physical…
We present high S/N spectra of the H-beta region in 17 intermediate redshift (0.85 le z le 2.5) quasars. The spectra represent first results of our campaign to test the redshift/luminosity robustness of the so-called Eigenvector 1 (E1)…
The interpretation of the main sequence of quasars has become a frontier subject in the last years. The consider the effect of a highly flattened, axially symmetric geometry for the broad-line region (BLR) on the parameters related to the…
The variability of the continuum spectral energy distribution has been analyzed for a complete magnitude-limited sample of quasars in Selected Area 57, observed at two epochs in the photographic $U$, $B_J$, $F$ and $N$ bands with the Mayall…
We compiled a sample of 60 quasars with spectroscopy on at least six epochs from the Sloan Digital Sky Survey (SDSS) to study the variabilities of the spectral shape, the continuum and the emission lines luminosity. In this paper, we…
We make use of individual (epoch) detection data from the Pan-STARRS 3Pi survey for 2863 optical ICRF3 counterparts in the five wavelength bands g, r, i, z, and y, published as part of the Data Release 2. A dedicated method based on the…
This paper presents results of a search for short-term variability in the optical band of selected high-luminosity, high-redshift radio-quiet quasars. Each quasar has been monitored typically for 2 - 4 hours with a time resolution of 2 - 5…
The brightest southern quasar above redshift $z=1$, HE 0515$-$4414, with its strong intervening metal absorption-line system at $z_{abs}=1.1508$, provides a unique opportunity to precisely measure or limit relative variations in the…
Using a large sample of Type 1 AGN spectra, we investigated the complex structure of the Fe II emission region in order to understand the atomic processes responsible for the enhancement of the Fe II emission. We explored correlations…
We report on a study that finds a positive correlation between black hole mass and variability amplitude in quasars. Roughly 100 quasars at z<0.75 were selected by matching objects from the QUEST1 Variability Survey with broad-lined objects…
We characterize the optical variability of quasars in the intermediate Palomar Transient Factory (iPTF) and Palomar Transient Factory (PTF) surveys. We re-calibrate the $r$-band light curves for $\sim$28,000 luminous, broad-line AGNs from…
We study the optical light curves - primarily probing the variable emission from the accretion disk - of ~ 900 extreme variability quasars (EVQs, with maximum flux variations more than 1 mag) over an observed-frame baseline of ~ 16 years…
In order to investigate the dependence of quasar variability on fundamental physical parameters like black hole mass, we have matched quasars from the QUEST1 Variability Survey with broad-lined objects from the Sloan Digital Sky Survey. The…
We present new clues to the problem of the radio loudness dichotomy arising from an extensive search for intranight optical variability in seven sets of optically luminous radio-quiet quasars and (radio-loud) BL Lacertae objects, which are…