Related papers: Optical variability of ICRF3 quasars in the Pan-ST…

Using the light curve time series data for more than 11.7 million variable sources published in the Gaia Data Release 3, the average magnitudes, colors, and variability parameters have been computed for 0.836 million Gaia CRF objects, which…

We present an analysis of quasar variability from data collected during a photometric monitoring of 50 objects carried out at CNPq/Laboratorio Nacional de Astrofisica, Brazil, between March 1993 and July 1996. A distinctive feature of this…

We present an update of 3C 273's database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the multiwavelength properties of this quasar,especially…

We have obtained single-epoch optical photometry for 201 quasars, taken from the FIRST Bright Quasar Survey, which span a wide range in radio loudness. Comparison with the magnitudes of these objects on the POSS-I plates provides by far the…

The identifications of quasars in the redshift range 2.2<z<3 are known to be very inefficient as their optical colors are indistinguishable from those of stars. Recent studies have proposed to use optical variability or near-IR colors to…

Low-frequency radio surveys are ideal for selecting orientation-independent samples of extragalactic sources because the sample members are selected by virtue of their isotropic steep-spectrum extended emission. We use the new 7C Redshift…

The variability of 30 PG quasars has been observed in the red band during three years. A rest-frame structure function analysis shows an increase of variability with the time interval up to 0.2 mag r.m.s. after two years. A comparison with…

In previous studies we have shown that the optical variability of quasars increases, on average, with redshift. We explained this dependance in terms of a hardening of the spectrum during bright phases, coupled with the increase of the…

The ensemble variability properties of nearly 23,000 quasars are studied using the Palomar-QUEST Survey. The survey has covered 15,000 square degrees multiple times over 3.5 years using 7 optical filters, and has been calibrated…

Amid rapid advances in time-domain astronomy, multi-wavelength (e.g., optical and infrared) time-domain studies of quasars remain scarce. Here we present a systematic analysis of four quasars initially selected by their Ks-band variability…

We quantify quasar color-variability using an unprecedented variability database - ugriz photometry of 9093 quasars from SDSS Stripe 82, observed over 8 years at ~60 epochs each. We confirm previous reports that quasars become bluer when…

We have monitored the quasar 3C 273 in optical $V$, $R$ and $I$ bands from 2005 to 2016. Intraday variability (IDV) is detected on seven nights. The variability amplitudes for most of nights are less than 10\% and four nights more than…

This work aimed to find the relationship between quasars' optical variability and spectral features to reveal the regularity behind the random variation. It is known that quasar's FeII/Hbeta flux ratio and equivalent width of [OIII]5007 are…

We present a comprehensive analysis of Chandra X-ray observations of 15 young radio quasars at redshifts $4.5 < z < 5.0$. All sources are detected in the $0.5-7.0$ keV energy band. Emission spectra are extracted, and the average photon…

Quasars are variable and their variability can both constrain their physical properties and help to identify them. We look for ways to efficiently identify quasars exhibiting consistent variability over multi-year time-scales, based on a…

Aims. The main purpose of this paper is to study time delays between the light variations in different wavebands for a sample of quasars. Measuring a reliable time delay for a large number of quasars may help constraint the models of their…

We examine the relationship between source position stability and astrophysical properties of radio-loud quasars making up the International Celestial Reference Frame. Understanding this relationship is important for improving quasar…

We present three new Chandra X-ray epochs along with new ground-based optical-UV observations as the third installment in a time-series analysis of four high-redshift ($z\sim4.1-4.4$) radio-quiet quasars (RQQs). In total, we present nine…

In this paper we review the basic Poissonian formulation of quasar variability, using it as a mathematical tool to extract relevant parameters such as the energy, rate and lifetimes of the flares through the analysis of observed light…

We present an analysis of X-ray variability in a sample of 156 radio quiet quasars taken from the ROSAT archive, covering a redshift range 0.1 < z < 4.1. A maximum likelihood method is used to constrain the amplitude of variability in these…