Related papers: X-ray transient AGN and galaxies
Models of X-ray reverberation from extended coronae are developed from general relativistic ray tracing simulations. Reverberation lags between correlated variability in the directly observed continuum emission and that reflected from the…
Active galactic nuclei (AGN) are complex phenomena. At the heart of an AGN is a relativistic accretion disk around a spinning supermassive black hole (SMBH) with an X-ray emitting corona and, sometimes, a relativistic jet. On larger scales,…
We report the discovery of a highly X-ray variable AGN, RX J2217.9-5941. This object was bright during the ROSAT All-Sky Survey (RASS), during which a decrease in the count rate by a factor of 12 was observed. It was found to be much…
Strongly magnetized, accreting neutron stars show periodic and aperiodic variability over a wide range of time scales. By obtaining spectral and timing information on these different time scales, we can have a closer look into the physics…
Seyfert galaxies and quasars were first discovered through optical and radio techniques, but in recent years high-energy emission, that can penetrate central gas and dust, has become essentially the defining characteristic of an AGN. AGNs…
In this review I briefly describe the latest advances in studies of aperiodic variability of accreting X-ray binaries and outline the model which currently describe the majority of observational appearances of variability of accreting…
Although a multitude of studies have focused on targeted observations of Galactic X-ray transients, blind surveys and population studies have been limited. We have used the ROSAT, eROSITA and Gaia source catalogs to find Galactic X-ray…
We measure the optical variability in $\sim$ 16500 low-redshift (z $\sim$ 0.1) galaxies to map the relations between AGN activity and galaxy stellar mass, specific star-formation rate, half-light radius and bulge-to-total ratio. To do this,…
We present the drastic transformation of the X-ray properties of the active galactic nucleus 1ES 1927+654, following a changing-look event. After the optical/UV outburst the power-law component, produced in the X-ray corona, disappeared,…
The nuclear regions of active galactic nuclei (AGNs) likely host clumpy clouds that occasionally obscure the central X-ray source, causing eclipse events. These events offer a unique opportunity to study the properties and origins of such…
To provide insight into the apparent mismatch between the optical and X-ray absorption properties observed in 10-30 % of Active Galactic Nuclei (AGN), we have conducted a detailed study of two X-ray unabsorbed AGN with a type-2 optical…
Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 10$^{39}$ erg s$^{-1}$. The average number of ULXs per galaxy is still not well constrained, especially given the uncertainty on the…
The disks of Active Galactic Nuclei (AGNs) have emerged as rich environments for the production and capture of stars and the compact objects that they leave behind. These stars produce long Gamma-Ray Bursts (LGRBs) at their deaths, while…
Recent X-ray observations have detected a class of very faint X-ray transients in the Galaxy which probably reveal a previously unrecognised type of accretion on to neutron stars or black holes. We show that these systems cannot have…
Fast X-ray transients (FXTs) with timescales from seconds to hours have been seen by numerous space instruments. We have assembled archival data from Ariel-5, HEAO-1 (A-1 and A-2), WATCH, ROSAT, and Einstein to produce a global…
Accretion discs around black holes power some of the most luminous objects in the Universe. Discs that are misaligned to the black hole spin can become warped over time by Lense-Thirring precession. Recent work has shown that strongly…
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…
In recent years deep X-ray and infrared surveys have provided an efficient way to find accreting supermassive black holes, otherwise known as active galactic nuclei (AGN), in the young universe. Such surveys can, unlike optical surveys,…
Relativistically blurred reflection from the accretion disc provides a powerful probe of the extreme environments close to supermassive black holes; the inner regions of the accretion flow and the corona that produces the intense X-ray…
We consider transient behavior in low-mass X-ray binaries. In short-period neutron-star systems (orbital period less than ~ 1d) irradiation of the accretion disk by the central source suppresses this except at very low mass transfer rates.…