Related papers: Optical Continuum Variability of the Active Galaxy…

We present results of a 3-month combined X-ray/UV/optical monitoring campaign of the Seyfert 1 galaxy NGC 6814. The object was monitored by Swift from June through August 2012 in the X-ray and UV bands and by the Liverpool Telescope from…

Lags measured from correlated X-ray/UV/optical monitoring of AGN allow us to determine whether UV/optical variability is driven by reprocessing of X-rays or X-ray variability is driven by UV/optical seed photon variations. We present the…

Many intermediate-mass close binaries exhibit photometric cycles longer than their orbital periods, likely related to accretion-disk variability. Previous studies indicate that historical light curves (LC) provide key constraints on disk…

The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys have been highly effective at selecting active galactic nuclei (AGN). However, cosmologically distant low-luminosity AGN (LLAGN) have remained a challenge to identify…

We report the discovery of a linear relationship between the root-mean-square (rms) variability amplitude and the mean flux in the accreting white dwarf binary system MV Lyrae. Our lightcurve, obtained with the Kepler satellite, spans 633…

We present optical continuum lags for two Seyfert 1 galaxies, MCG+08-11-011 and NGC 2617, using monitoring data from a reverberation mapping campaign carried out in 2014. Our light curves span the ugriz filters over four months, with median…

We present the results of a continuum reverberation mapping study of the radio-quiet Seyfert 1 galaxy IRAS 09149-6206. The analysis was performed using X-ray, UV and optical observations made with the {\em Swift} telescope between January…

We discuss a model of X-ray variability of active galactic nuclei (AGN). We consider multiple spots which originate on the surface of an accretion disk following intense irradiation by coronal flares. The spots move with the disk around the…

We have carried out a systematic analysis of the nearby (z=0.0279) active galaxy Zw 229.015 using multi-epoch, multi-instrument and deep pointed observations with XMM-Newton, Suzaku, Swift and NuSTAR. Spectral and temporal variability are…

The physical mechanism for triggering the changing-look phenomenon in active galactic nuclei (AGNs) is still unclear. We explore this issue based on the multi-wavelength spectral and flux variations for a changing-look AGN Mrk~1018 with…

We present a detailed spectral study of the narrow-line Seyfert~1 galaxy, Markarian~335, using eight epoch observations made between 2013 and 2020 with the Nuclear Spectroscopic Telescope Array. The source was variable during this period…

Data from the first three years of RXTE observations have been systematically analyzed to yield a set of 300 day, 2-10 keV light curves with similarly uniform, ~5 day sampling, for a total of nine Seyfert 1 galaxies. This is the first X-ray…

We present the results of our studies of the aperiodic optical flux variability for SS Cyg, an accreting binary systemwith a white dwarf. The main set of observational data presented here was obtained with the ANDOR/iXon DU-888 photometer…

Accretion disks around supermassive black holes in active galactic nuclei produce continuum radiation at ultraviolet and optical wavelengths. Physical processes in the accretion flow lead to stochastic variability of this emission on a wide…

We present optical observations of the low-luminosity Seyfert 1 nucleus of NGC 4395, as part of a multiwavelength reverberation-mapping program. Observations were carried out over two nights in 2004 April at Lick, Wise, and Kitt Peak…

The supersoft X-ray binary RX J0513.9-6951 shows cyclic changes between optical-low / X-ray-on states and optical-high / X-ray-off states. It is supposed to be accreting close to the Eddington-critical limit and driven by "accretion wind…

Multi-wavelength monitoring of Mrk 335 with Swift between 2007-2019 are used to construct annual spectral energy distributions and track year-to-year changes. Non-contemporaneous archival data prior to 2007 are used to build a bright state…

We analyze the X-ray, optical, and mid-infrared data of a "changing-look" Seyfert galaxy \sdssj15 at $z\simeq0.086$. Over a period of one decade (2009 - 2018), its broad H$\alpha$ line intensity increased by a factor of $\sim$4. Meanwhile,…

Broad Balmer emission lines in active galactic nuclei (AGN) may display dramatic changes in amplitude, even disappearance and re-appearance in some sources. As a nearby galaxy at a redshift of z = 0.0264, Mrk 590 suffered such a cycle of…

(Abridged) Active galactic nuclei show a wealth of interesting physical processes, some of which are poorly understood. We want to address a number of open questions, including the location and physics of the outflow from AGN, the nature of…