Related papers: Simulating the timescale dependent color variation…
Accretion discs are fundamental to much of astronomy. They can occur around stars both young and old, around compact objects they provide a window into the extremes of physics, and around supermassive black holes in galaxy centres they…
A sample of quasars has been recently assembled to investigate the non-linear relation between their monochromatic luminosities at 2500{\AA}, and 2 keV and to exploit quasars as a new class of standardized candles. The use of this technique…
In addition to coherent pulsation, many accreting neutron stars exhibit flaring activity and strong aperiodic variability on time scales similar to or shorter than their pulsation period. Such a behavior shows that the accretion flow in the…
Using 16,421 spectra from a sample of 340 quasars ($1.62<z<3.30$) from the SDSS Reverberation Mapping Project, we present an analysis of quasar spectral variability. We confirm the intrinsic Baldwin Effect and brighter-means-bluer trends in…
Fourier power spectra and phases of a signal from a large number of radiating sources orbiting around a black hole are investigated. It is assumed that the individual sources (bright spots) are located in an accretion disc and their…
Long-term observations have shown that black hole X-ray binaries exhibit strong, aperiodic variability on time-scales of a few milliseconds to seconds. The observed light curves display various characteristic features like a log-normal…
Context: Variations in the mass accretion rate appear to be responsible for the rapid transitions in spectral type that are observed in increasingly more active galactic nuclei (AGNs). These objects are now labeled "changing-look" AGNs and…
We measure long (2200-4000 ang) and short (1450-2200 ang) wavelength spectral slopes \alpha (F_\nu proportional to \nu^\alpha) for quasar spectra from the Sloan Digital Sky Survey. The long and short wavelength slopes are computed from 3646…
The amplitude and phase modulation observed in a significant fraction of the RR Lyrae variables - the Blazhko effect - represents a long-standing enigma in stellar pulsation theory. No satisfactory explanation for the Blazhko effect has…
We study the long-term ($\approx$30 years) radio variability of 43 radio bright AGNs by exploiting the data base of the University of Michigan Radio Astronomy Observatory (UMRAO) monitoring program. We model the periodograms (temporal power…
Intensive monitoring campaigns have recently attempted to measure the time delays between multiple images of gravitational lenses. Some of the resulting light-curves show puzzling low-level, rapid variability which is unique to individual…
A tight non-linear relation exists between the X-ray and UV emission in quasars (i.e. $L_{\rm X}\propto L_{\rm UV}^{\gamma}$), with a dispersion of $\sim$0.2~dex over $\sim$3~orders of magnitude in luminosity. Here we propose a modified…
The light scattered by an extrasolar Earth-like planet's surface and atmosphere will vary in intensity and color as the planet rotates; the resulting light curve will contain information about the planet's properties. Since most of the…
We investigate the luminosity and redshift dependence of the quasar continuum by means of composite spectrum using a large non-BAL radio-quiet quasar sample drawn from the Sloan Digital Sky Survey. Quasar continuum slopes in the UV-Opt band…
We investigate aperiodic X-ray flux variability in accreting highly magnetized neutron stars - X-ray pulsars (XRPs). The X-ray variability is largely determined by mass accretion rate fluctuations at the NS surface, which replicate…
Universal to black hole X-ray binaries, the high-frequency soft lag gets longer during the hard-to-intermediate state transition, evolving from ${\lesssim}1~{\rm ms}$ to ${\sim}10~{\rm ms}$. The soft lag production mechanism is thermal disk…
We discuss the issues of stability of accretion disks that may undergo the limit-cycle oscillations due to the two main types of thermal-viscous instabilities. These are induced either by the domination of radiation pressure in the…
Ultraluminous X-ray sources (ULXs) with luminosities lying between ~3x10^{39} - 2x10^{40} erg/s represent a contentious sample of objects as their brightness, together with a lack of unambiguous mass estimates for the vast majority of the…
In this work we have developed a new stochastic model for the fluctuations in lightcurves of accreting black holes. The model is based on a linear combination of stochastic processes and is also the solution to the linear diffusion equation…
Changing-look active galactic nuclei (CL AGNs) show large changes in luminosity and optical spectral state on time-scales of a few years, and provide a valuable probe of time-dependent accretion in the disc-BLR-torus system. We present a…