Related papers: Structure function of the UV variability of Q0957+…
Quasars have long been known to be variable sources at all wavelengths. Their optical variability is stochastic, can be due to a variety of physical mechanisms, and is well-described statistically in terms of a damped random walk model. The…
The gravitational lens 0957+561 was monitored with the Very Large Array from 1979 to 1997. The 6 cm light curve data from 1995-1997 and the 4 cm data from 1990-1997 are reported here. At 4 cm, the intrinsic source variations occur earlier…
We reported the result of long term optical variability of the blazar 4C 29.45 (QSO 1156+295, Ton 599), carried out optical photometric observations in Johnson V, Cousins RI passbands during April 1997 to March 2002 using the 1.56 meter…
We present new spectroscopic and polarimetric observations of the first discovered gravitational lens Q0957+561 obtained with the 6m telescope of the Special Astrophysical Observatory (SAO, Russia). We explore spectropolarimetric parameters…
The variability of active galactic nuclei (AGN) has long held the promise of shedding light on their detailed structure, and possibly other astrophysical phenonema. Different emission mechanisms lead to different patterns of variability in…
Context: In April 2013, the nearby (z=0.031) TeV blazar, Mkn 421, showed one of the largest flares in X-rays since the past decade. Aim: To study all multiwavelength data available during MJD 56392 to 56403, with special emphasis on X-ray…
Based on a 10 years sample of gamma-ray flares of FSRQs collected with FERMI and AGILE, I report on this proceeding the advance on a statistical study of variability for a sample of more than 300 FSRQs. I will focus on waiting time between…
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…
Studying transversal structure in extragalactic jets is crucial for understanding their physics. The Japanese led space VLBI project VSOP has offered arguably the best opportunity for such studies, by reaching baseline lengths of up to…
Context. We present the light curves of six BL Lac objects, PKS 0537-441, PKS 0735+17, OJ 287, PKS 2005-489, PKS 2155-304, W Comae, and of the flat spectrum radio quasar PKS 1510-089, as a part of a photometric monitoring program in the…
This paper reports on the extreme ultraviolet (EUV) spectrum of three low redshift ($z \sim 0.6$) radio loud quasars, 3C 95, 3C 57 and PKS 0405-123. The spectra were obtained with the Cosmic Origins Spectrograph (COS) of the Hubble Space…
We present results of five years of optical (UBVRI) observations of the very-high-energy gamma-ray blazar 1ES 1011+496 at the MDM Observatory. We calibrated UBVRI magnitudes of five comparison stars in the field of the object. Most of our…
Context. The origin of blazar variability, seen from radio up to gamma rays, is still a heavily debated matter and broadband flares offer a unique testbed towards a better understanding of these extreme objects. Such an energetic outburst…
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 present results from monitoring the multi-waveband flux, linear polarization, and parsec-scale structure of the quasar PKS 1510-089, concentrating on eight major gamma-ray flares that occurred during the interval 2009.0-2009.5. The…
We present a detailed temporal and spectral analysis of the blazar S5\,1044+71 using multi-wavelength data obtained from the \emph{Fermi}-LAT and Swift-XRT/UVOT telescopes. Applying the Bayesian block algorithm to the 3-day binned…
Context: Extensive, multi-wavelength monitoring campaigns of nearby and higher redshift active galactic nuclei (AGN) have shown that the UV/optical variations are well correlated with time delays which increase with increasing wavelength.…
Within the framework of the internal shock model, we study the luminosity and the variability in gamma-ray bursts from collimated fireballs. In particular we pay attention to the role of the photosphere due to $e^\pm$ pairs produced by…
We present new brightness monitoring observations of the 4 components of gravitationally lensed system Q2237+0305, which show detection of an intrinsic quasar brightness fluctuation at a time of subdued microlensing activity, between June…
The well-known anti-correlation between the optical/ultraviolet (UV) emission line equivalent widths of active galactic nuclei and the continuum luminosity (the so-called Baldwin effect) is a long-standing puzzle. One common hypothesis is…