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…
Accretion disk winds in active galactic nuclei: X-ray observations, models, and feedback
Tombesi, F.
Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this ``quasar mode'' feedback came from the recent X-ray observation of a …
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 …
Andromeda IV, a solitary gas-rich dwarf galaxy
Rizzi, L.; Sharina, M. E.; Karachentsev, I. D. +4 more
Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm H I line. We determine the galaxy distance of 7.17{±}0.31 Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of -12.…
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…
Gaia
Cacciari, C.; Pancino, E.; Bellazzini, M.
A review of the Gaia mission and its science performance after one year of operations will be presented, and the contribution to reconstructing the history of the Milky Way will be outlined.
Towards 21st century stellar models: Star clusters, supercomputing and asteroseismology
Christensen-Dalsgaard, J.; Stello, D.; D'Orazi, V. +8 more
Stellar models provide a vital basis for many aspects of astronomy and astrophysics. Recent advances in observational astronomy - through asteroseismology, precision photometry, high-resolution spectroscopy, and large-scale surveys - are placing stellar models under greater quantitative scrutiny than ever. The model limitations are being exposed a…
Spectral components in black hole X-ray binaries
Malzac, J.
This paper summarises our current understanding of the spectral continuum components observed in black hole X-ray binaries. The consequences for theoretical models are discussed with an emphasis on the constraints set by observations on the nature of the X-ray corona in different spectral states.
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…