Related papers: Ultraviolet and X-ray variability of active galact…
We present results of recurrence analysis of 46 active galactic nuclei (AGN) using light curves from the 157-month catalog of the Swift Burst Alert Telescope (BAT) in the 14-150 keV band. We generate recurrence plots and compute recurrence…
The dependence of the long-term optical/UV variability on the spectral and the fundamental physical parameters for radio-quiet active galactic nuclei (AGNs) is investigated. The multi-epoch repeated photometric scanning data in the…
We investigate the properties of a variability-selected complete sample of AGN in order to identify the mechanisms which cause large amplitude X-ray variability on time scales of years. A complete sample of 24 sources was constructed, from…
$\require{mediawiki-texvc}$ We study accretion disk emission from eight Seyfert $1 - 1.5$ active galactic nuclei (AGN) using far ultra-violet ($1300-1800$ ${\AA}$) slit-less grating spectra acquired with AstroSat/UVIT. We correct for the…
The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of…
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 present 1.8 years of near-daily Swift monitoring of the bright, strongly variable Type 1 AGN Fairall 9. Totaling 575 successful visits, this is the largest such campaign reported to date. Variations within the UV/optical are…
X-ray variability in Active Galactic Nuclei (AGN) is commonly analysed in terms of the Power Spectral Density (PSD). The break observed in the power spectrum can be interpreted as a characteristic X-ray variability time scale. Here we study…
Context. Variability is a ubiquitous feature of active galactic nuclei (AGNs), and the characterisation of the variability is crucial to constrain its physical mechanism and proper applications in AGN studies. The advent of all-sky and…
The black-hole binary, V404 Cygni, went into outburst in June 2015, after 26 years of X-ray quiescence. We observed the outburst with the Neil Gehrels Swift observatory. We present optical/UV observations taken with the Swift Ultra-violet…
We report the results obtained by a systematic, broadband (0.5--150 keV) X-ray spectral analysis of moderately obscured (Compton-thin; $22 \leq \log N_{\rm H} < 24$) active galactic nuclei (AGNs) observed with Suzaku and Swift/Burst Alert…
The cosmological evolution of X-ray-selected and optically selected Active Galactic Nuclei (AGNs) show different behaviours interpreted in terms of two different populations. The difference is evident mainly for low luminosity AGNs…
We use mid-infrared variability in galaxies to search for active galactic nuclei (AGN) in the local universe. We use a sample of 10,220 galaxies from the Mapping Nearby Galaxies at APO (MaNGA) survey, part of the Sloan Digital Sky Survey…
We study spectral variability of 11 ultraluminous X-ray sources (ULX) using archived XMM-Newton and Chandra observations. We use three models to describe the observed spectra; a power-law, a multi-colour disk (MCD) and a combination of…
The optical-ultraviolet continuum from active galactic nuclei (AGN) seem to originate from optically thick and/or thin disks, and occasionally from associated circumnuclear starburst regions. These different possible origins can, in…
We present the results of the analysis of the first 9 months of data of the Swift BAT survey of AGN in the 14-195 keV band. Using archival X-ray data or follow-up Swift XRT observations, we have identified 129 (103 AGN) of 130 objects…
We present new XMM-Newton observations of two luminous and high accretion-rate radio-quiet active galactic nuclei (AGNs) at z~2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties as well as…
Using three epochs of VLA observations of the Galactic Plane in the first quadrant taken ~15 years apart, we have conducted a search for a population of variable Galactic radio emitters in the flux density range 1-100 mJy at 6 cm. We find…
We present the results of our search for highly variable active galactic nuclei (AGNs) the X-ray flux from which changed by more than an order of magnitude during the SRG/eROSITA all-sky survey. Using the eROSITA data obtained in the period…
We present a systematic investigation of extremely X-ray variable active galactic nuclei (AGNs) in the $\approx 5.3~{\rm deg}^2$ XMM-SERVS XMM-LSS region. Eight variable AGNs are identified with rest-frame 2 keV flux density variability…