Related papers: Long-term optical flux and colour variability in q…

We studied the optical variability of 241 BL Lacs and 83 flat-spectrum radio quasars (FSRQ) from the 4LAC catalog using data from the Tomo-e Gozen Northern Sky Transient Survey, with $\sim$ 50 epochs per blazar on average. We excluded…

We present new spectroscopic observations that are part of our continuing monitoring campaign of 88 quasars at z<0.7 whose broad H$\beta$ lines are offset from their systemic redshifts by a few thousand km/s. These quasars have been…

Microlensing by stars in the lens galaxy of a gravitationally lensed quasar is a phenomenon that can selectively magnify quasar subregions, producing observable changes in the continuum brightness or distortions in the emission line…

We analyze the long-term (rest-frame 3-30 yr) X-Ray variability of eleven broad absorption line (BAL) quasars, mainly to constrain the variation properties of the X-Ray absorbing shielding gas that is thought to play a critical role in BAL…

Quasi-stellar objects (QSOs) are a basis for an absolute reference system for astrometric studies. There is a need for creating such system behind nearby galaxies, to facilitate the measuring of the proper motions of these galaxies.…

Aims: We aim at investigating the time-behaviour of a sample of gamma-ray blazars. We present the results from a 13 month-long optical photometry monitoring campaign of the blazars PKS 0048-097, PKS 0754+100, HB89 0827+243, PKS 0851+202,…

We present high S/N UV spectra for eight quasars at z $\sim$ 3 obtained with VLT/FORS. The spectra enable us to analyze in detail the strong and weak emission features in the rest-frame range 1300-2000 A of each source (Ciii]$\lambda$1909,…

Recent work has found evidence for a difference in the bias and dark matter halo masses of WISE-selected obscured and unobscured quasars, implying a distinction between these populations beyond random line-of-sight effects. However, the…

We review results from our monitoring observations of several lensed quasars performed in the optical, UV, and X-ray bands. Modeling of the multi-wavelength light curves provides constraints on the extent of the optical, UV, and X-ray…

Given the anisotropic emission from quasar accretion discs, their viewing angle affects estimates of the quasar luminosity, black-hole mass and Eddington ratio. Discs appear overluminous when viewed pole-on and underluminous when viewed at…

We present the first measurement of the spatial clustering of mid-infrared selected obscured and unobscured quasars, using a sample in the redshift range 0.7 < z < 1.8 selected from the 9 deg^2 Bootes multiwavelength survey. Recently the…

Blazars, a subset of powerful active galactic nuclei, feature relativistic jets that shine in a broadband electromagnetic radiation, e. g. from radio to TeV emission. Here I present the results of the studies that explore gamma-ray and…

We present a well-designed sample of more than 1000 type 1 quasars at $3.5<z<5$ and derive UV quasar luminosity functions (QLFs) in this redshift range. These quasars were selected using the Sloan Digital Sky Survey (SDSS) imaging data in…

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz…

We monitored the BL Lac object S5 0716+714 in the optical band during October 2008, December 2008 and February 2009 with a best temporal resolution of about 5 minutes in the BVRI bands. Four fast flares were observed with amplitudes ranging…

We present variability and multi-wavelength photometric information for the 933 known quasars in the QUEST Variability Survey. These quasars are grouped into variable and non-variable populations based on measured variability confidence…

The non-linear relation between the X-ray and ultraviolet (UV) luminosity in quasars has been used to derive quasar distances and to build a Hubble diagram at redshifts up to $z\sim$ 7. This cosmological application is based on the…

We present the first results from long-term high-cadence spectroscopic monitoring of 15 PG quasars with relatively strong Fe II emission as a part of a broader reverberation mapping campaign performed with the Calar Alto Observatory 2.2m…

We apply a simple statistical method (Derenzo & Hildebrand 1969) to estimating the completeness of quasar surveys. It requires that an area has been covered by two or more, preferably different, selection techniques. We use three suitable…

We present the discovery of two z > 6 quasars, selected as i band dropouts in the VST ATLAS survey. Our first quasar has redshift, z = 6.31 \pm 0.03, z band magnitude, z_AB = 19.63 \pm 0.08 and rest frame 1450A absolute magnitude, M_1450 =…