Search Publications
The origin of UV-optical variability in AGN and test of disc models: XMM-Newton and ground-based observations of NGC 4395
Gandhi, P.; Netzer, H.; Peterson, B. M. +12 more
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 observational programmes, particularly of NGC 5548 with Swift, have shown that the UV/optical variations lag behi…
High ionisation absorption in low mass X-ray binaries
Merloni, A.; Bianchi, S.; Ponti, G. +3 more
The advent of the new generation of X-ray telescopes yielded a significant step forward in our understanding of ionised absorption generated in the accretion discs of X-ray binaries. It has become evident that these relatively weak and narrow absorption features, sporadically present in the X-ray spectra of some systems, are actually the signature…
Quasi periodic oscillations in active galactic nuclei
Kara, E.; Fabian, A.; Middleton, M. +3 more
Quasi-periodic oscillations (QPOs) are coherent peaks of variability power observed in the X-ray power spectra (PSDs) of stellar mass X-ray binaries (XRBs). A scale invariance of the accretion process implies they should be present in the active galactic nuclei. The first robust detection was a ∼ 1 h periodicity in the Seyfert galaxy RE J1034+396 …
A global look at X-ray time lags in Seyfert galaxies
Kara, E.; Fabian, A.; Alston, W.
X-ray reverberation, where light-travel time delays map out the compact geometry around the inner accretion flow in supermassive black holes, has been discovered in several of the brightest, most variable and well-known bare Seyfert galaxies. In this work, we expand the study of X-ray time lags to all Seyfert galaxies in the XMM-Newton archive abo…
An intermediate-mass black hole candidate in M51?
Earnshaw, H. M.
We present the current results of an investigation into M51 ULX-7, using archival data from XMM-Newton, Chandra and NuSTAR, and optical and radio data from HST and VLA. The source has a consistently hard power-law X-ray spectrum and high short-term variability. This is unusual variability behaviour for a ULX, as we would expect highly variable ULX…
The peculiar megamaser AGN NGC 1194: Comparison with the warped disk candidates NGC 1068 and NGC 4258
Vasylenko, A.; Fedorova , E.; Hnatyk, B. I. +1 more
We analyze the X-ray properties of the Compton-thick Seyfert 1.9 radio quiet AGN in NGC 1194 using INTEGRAL (ISGRI), XMM-Newton (EPIC), Swift (BAT and XRT), and Suzaku (XIS) observations. There is a set of Fe-K lines in the NGC 1194 spectrum with complex relativistic profiles that can be considered as a sign of either a warped Bardeen-Petterson ac…
Eclipsing the innermost accretion disc regions in AGN
Miniutti, G.; Dovčiak, M.; Sanfrutos, M. +1 more
Variable X-ray absorption has been observed in active galactic nuclei (AGN) on several time scales. Observations allow us to identify the absorber with clouds associated either with the clumpy torus (parsec scales, long timescales) or with the broad line region (BLR) (short timescales). In the latter, the cloud size has been estimated to be of the…
Broadband short term X-ray variability of the quasar PDS 456
Tombesi, F.; Reeves, J. N.; Braito, V. +4 more
We present a detailed analysis of a recent 500 ks net exposure Suzaku observation, carried out in 2013, of the nearby (z=0.184) luminous (L_bol∼1047 erg s-1) quasar PDS 456 in which the X-ray flux was unusually low. The short term X-ray spectral variability has been interpreted in terms of variable absorption and/or intrinsic…
Absorption from a multi-layer circumnuclear medium and reflection from the accretion disc in NGC 1365
Risaliti, G.
NGC 1365 hosts an X-ray obscured AGN known for both its variable absorption and its relativistic features in the reflection component. Recent simultaneous observations performed by XMM-Newton and NuSTAR caught the source in a rare, nearly unobscured state, revealing the presence of a warm absorber and a neutral, but low column density (∼ 1022…
High-energy monitoring of Seyfert galaxies: The case of NGC 4593
Bianchi, S.; Cappi, M.; Ponti, G. +6 more
We discuss preliminary results from a joint XMM-Newton and NuSTAR monitoring program on the active galactic nucleus NGC 4593, consisting of 5 × 20 ks observations, spaced by two days, performed in January 2015. The source is found to be variable, both in flux and spectral shape, on time scales as short as a few ks. The spectrum clearly softens whe…