Search Publications
Unifying the observational diversity of isolated neutron stars via magneto-thermal evolution models
Rea, N.; Perna, R.; Pons, J. A. +3 more
Observations of magnetars and some of the high magnetic field pulsars have shown that their thermal luminosity is systematically higher than that of classical radio-pulsars, thus confirming the idea that magnetic fields are involved in their X-ray emission. Here we present the results of 2D simulations of the fully coupled evolution of temperature…
Irradiation of an accretion disc by a jet: general properties and implications for spin measurements of black holes
Reynolds, C. S.; Dauser, T.; Wilms, J. +5 more
X-ray irradiation of the accretion disc leads to strong reflection features, which are then broadened and distorted by relativistic effects. We present a detailed, general relativistic approach to model this irradiation for different geometries of the primary X-ray source. These geometries include the standard point source on the rotational axis a…
Suzaku observations of `bare' active galactic nuclei
Fabian, A. C.; Nardini, E.; Reis, R. C. +2 more
We present an X-ray spectral analysis of a large sample of 25 `bare' active galactic nuclei (AGN), sources with little or no complicating intrinsic absorption, observed with Suzaku. Our work focuses on studying the potential contribution from relativistic disc reflection and examining the implications of this interpretation for the intrinsic spect…
Discovery of a relation between black hole mass and soft X-ray time lags in active galactic nuclei
Cappi, M.; Ponti, G.; Fabian, A. C. +5 more
We carried out a systematic analysis of time lags between X-ray energy bands in a large sample (32 sources) of unabsorbed, radio quiet active galactic nuclei (AGN), observed by XMM-Newton. The analysis of X-ray lags (up to the highest/shortest frequencies/time-scales), is performed in the Fourier-frequency domain, between energy bands where the so…
Generating artificial light curves: revisited and updated
Papadakis, I. E.; Emmanoulopoulos, D.; McHardy, I. M.
The production of artificial light curves with known statistical and variability properties is of great importance in astrophysics. Consolidating the confidence levels during cross-correlation studies, understanding the artefacts induced by sampling irregularities, establishing detection limits for future observatories are just some of the applica…
The ultraluminous state revisited: fractional variability and spectral shape as diagnostics of super-Eddington accretion
Middleton, Matthew J.; Sutton, Andrew D.; Roberts, Timothy P.
Although we are nearing a consensus that most ultraluminous X-ray sources (ULXs) below 1041 erg s-1 represent stellar mass black holes accreting in a super-Eddington `ultraluminous' accretion state, little is yet established of the physics of this extreme accretion mode. Here, we use a combined X-ray spectral and timing analy…
A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys
Sanders, D. B.; Taniguchi, Y.; Alexander, D. M. +33 more
We present an investigation into how well the properties of the accretion flow on to a supermassive black hole may be coupled to those of the overlying hot corona. To do so, we specifically measure the characteristic spectral index, Γ, of a power-law energy distribution, over an energy range of 2-10 keV, for X-ray selected, broad-lined radio-quiet…
The UV and X-ray activity of the M dwarfs within 10 pc of the Sun
Liefke, C.; Micela, G.; Marino, A. +2 more
M dwarfs are the most numerous stars in the Galaxy. They are characterized by strong magnetic activity. The ensuing high-energy emission is crucial for the evolution of their planets and the eventual presence of life on them. We systematically study the X-ray and ultraviolet emission of a subsample of M dwarfs from a recent proper-motion survey, s…
Discovery of high-frequency iron K lags in Ark 564 and Mrk 335
Fabian, A. C.; Uttley, P.; Cackett, E. M. +3 more
We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate the frequency-dependent time lags for these two well-studied sources. We discover high-frequency Fe K lags in both sources, indicating that the red wing of the line precedes the rest-frame energy by roughly 100 and 150 s for Ark 564 and Mrk 335, respectively. Including the…
Long XMM observation of the narrow-line Seyfert 1 galaxy IRAS 13224-3809: rapid variability, high spin and a soft lag
Young, A. J.; Brandt, W. N.; Ponti, G. +21 more
The narrow-line Seyfert 1 galaxy IRAS 13224-3809 has been observed with XMM-Newton for 500 ks. The source is rapidly variable on time-scales down to a few 100 s. The spectrum shows strong broad Fe - K and L emission features which are interpreted as arising from reflection from the inner parts of an accretion disc around a rapidly spinning black h…