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To evaluate biological effects triggered by low levels of radiation, we established a uniquely sensitive experimental system to detect somatic mutations. By using the system, we found that mutant frequencies induced by X-rays were statistically significant at doses over 0.15 Gy, and a linear dose relationship with the mutant frequency was observed at doses over 0.15 Gy. The mutation spectra analysis revealed that mutation events generated by X-ray doses below 0.1 Gy were similar to those observed in unirradiated controls. In addition, a significant inflection point for both, the mutant frequency and the mutation spectra, was found at dose-rates around 11 mGy/day when cells were cultured in medium containing tritiated water. Because induced radiation-type events presented a clear dose/dose-rate dependency above the critical dose or the inflection point, these observations suggest that mutation events generated by radiation could change at a threshold dose-rate or a critical dose. [ABSTRACT FROM AUTHOR]

A comparison of the analysis of respirable crystalline silica direct-on-filter methods using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy was undertaken using 253 real workplace air samples from road construction and tunnelling, coal mining, and kitchen benchtop manufacturing in Australia. Using pure α-quartz standards, XRD and FT-IR direct-on-filter analyses produced identical test results, however, the real workplace samples showed a clear discrepancy between FT-IR and XRD results with on average a 9% positive bias of the FT-IR results. The cause of the positive bias was due to matrix interferences which was confirmed by using synthetic mixture air samples. Approximately a third of the data by direct-on-filter method using FT-IR was assessed to be invalid based on the peak height ratio criterion due to excessive interferences and weight overload limitations. The XRD method showed better results due to less interference from the common matrices. XRD could handle up to twice the sample loading and at higher loadings up to 7 mg when a correction was applied. It was also able to achieve a lower limit of detection of 2 µg filter−1 when a slower scan condition was utilized. [ABSTRACT FROM AUTHOR]

NGC 5548 was recently monitored intensively from NIR to X-rays as part of the STORM campaign. Its disc emission was found to lag behind the observed X-rays, while the measured time lag was increasing with wavelength. These results are consistent with the assumption that short-term variability in AGN emission is driven by the X-ray illumination of the accretion disc. In this work, we studied the power spectrum of UV/optical and X-ray emission of NGC 5548, using the data of the STORM campaign as well as previous Swift data, in order to investigate the relation between the UV/optical and X-ray variability and to examine its consistency with the above picture. We demonstrate that even the power spectrum results are compatible with a standard disc being illuminated by X-rays, with low accretion rates, but the details are not entirely consistent with the results from the modelling of the 'τ versus λ' relation. The differences indicate that the inner disc might be covered by a 'warm corona' which does not allow the detection of UV/optical emission from the inner disc. Finally, we found strong evidence that the UV emission of NGC 5548 is not stationary. [ABSTRACT FROM AUTHOR]

We present the results of X-ray spectral-timing analysis of a 90 ks XMM–Newton observation of the nearby, broad-line, early-type AGN NGC5273. The X-ray spectrum revealed the clear presence of a reflection component at high energies, with a clear signature of a narrow iron line at 6.4 keV, consistent with distant reflection. Applying a relativistic reflection model, we found only marginal evidence for a broader relativistic line component. However, cross-spectral analysis revealed that, between 4 and 6 × 10−4 Hz, the 5–8 keV band lagged the 2–3 keV band, implying reflection of the iron line from material close to the black hole. From the analysis of the lag-energy spectrum, we found a broad, but skewed line with a peak of ≈1000 s at 7.5 keV relative to the continuum, which we interpret as the iron line in the reverberation spectrum from an illuminated accretion disc. From the asymmetry in the shape of lag-energy spectrum, we also found that the source is consistent with having an inclination ≥45°. [ABSTRACT FROM AUTHOR]

Aims The present aims were firstly to coat metal implant material with a quorum sensing inhibitory thiophenone molecule, and secondly to assess the inhibitory effect on Staphylococcus epidermidis biofilm accumulation on thiophenone-coated coupons. Method and Results Thiophenone- and control-coated metal coupons were prepared by silane hydrolysis and dip coating. The linking of thiophenone to the surface was confirmed by X-ray photoelectron spectroscopy analyses. Biofilm by Staph. epidermidis, a frequent cause of implant-associated infections, was allowed to form under flowing conditions for 48 h. The biofilm accumulations were significantly reduced on the thiophenone-coated coupons. This was confirmed by confocal scanning microscopy. Conclusion This study showed for the first time how a synthetic thiophenone may be covalently linked to a stainless steel surface, and that biofilm accumulations on such surfaces are significantly reduced. Significance and Impact of the Study Functionalizing surfaces by covalent linking of thiophenones might open a wide array of applications. Thiophenone coating of medical implants represents a novel and promising approach to prevent implant-associated infections. [ABSTRACT FROM AUTHOR]

We report the results of detailed Monte Carlo simulations of the performance expected both at balloon altitudes and at the probable satellite orbit of a hard X-ray coded-aperture camera being developed for the Monitor e Imageador de RAios X (MIRAX) mission. Based on a thorough mass model of the instrument and detailed specifications of the spectra and angular dependence of the various relevant radiation fields at both the stratospheric and orbital environments, we have used the well-known package GEANT4 to simulate the instrumental background of the camera. We also show simulated images of source fields to be observed and calculated the detailed sensitivity of the instrument in both situations. The results reported here are especially important to researchers in this field considering that we provide important information, not easily found in the literature, on how to prepare input files and calculate crucial instrumental parameters to perform GEANT4 simulations for high-energy astrophysics space experiments. [ABSTRACT FROM AUTHOR]

PKS 2155-304 is one of the brightest extragalactic source in the X-ray and EUV bands, and is a prototype for the BL Lac class of objects. In this paper, we investigate the large-scale environment of this source using new multi-object as well as long-slit spectroscopy, together with archival spectra and optical images. We find clear evidence of a modest overdensity of galaxies at z = 0.116 10 ± 0.000 06, consistent with previous determinations of the BL Lac redshift. The galaxy group has a radial velocity dispersion of 250+80-40 km s-1 and a virial radius of 0.22 Mpc, yielding a role-of-thumb estimate of the virial mass of Mvir ~ 1.5 × 1013 M☉, i.e. one order of magnitude less than that observed in similar objects. This result hints towards a relatively wide diversity in the environmental properties of BL Lac objects. [ABSTRACT FROM AUTHOR]

Multi-Unit Spectroscopic Explorer (MUSE) observations of NGC 5813 reveal a complex structure in the velocity dispersion map, previously hinted at by SAURON observations. The structure is reminiscent of velocity dispersion maps of galaxies comprising two counterrotating discs, and might explain the existence of the kinematically distinct core (KDC). Further evidence for two counter-rotating components comes from the analysis of the higher moments of the stellar line-of-sight velocity distributions and fitting MUSE spectra with two separate Gaussian line-of-sight velocity distributions. The emission-line kinematics show evidence of being linked to the present cooling flows and the buoyant cavities seen in X-rays. We detect ionized gas in a nuclear disc-like structure, oriented like the KDC, which is, however, not directly related to the KDC. We build an axisymmetric Schwarzschild dynamical model, which shows that the MUSE kinematics can be reproduced well with two counter-rotating orbit families, characterized by relatively low angular momentum components, but clearly separated in integral phase space and with radially varying contributions. The model indicates that the counter-rotating components in NGC 5813 are not thin discs, but dynamically hot structures. Our findings give further evidence that KDCs in massive galaxies should not necessarily be considered as structurally or dynamically decoupled regions, but as the outcomes of the mixing of different orbital families, where the balance in the distribution ofmass of the orbital families is crucial. We discuss the formation of the KDC in NGC 5813 within the framework of gas accretion, binary mergers and formation of turbulent thick discs from cold streams at high redshift. [ABSTRACT FROM AUTHOR]

The dimensions of Fanaroff-Riley class I jets and the stellar densities at galactic centres imply that there will be numerous interactions between the jet and stellar winds. These may give rise to the observed diffuse and 'knotty' structure of the jets in the X-ray, and can also mass load the jets. We performed modelling of internal entrainment from stars intercepted by Centaurus A's jet, using stellar evolution- and wind codes. From photometry and a code-synthesized population of 12 Gyr (Z = 0.004), 3 Gyr (Z = 0.008) and 0-60 Myr (Z = 0.02) stars, appropriate for the parent elliptical NGC 5128, the total number of stars in the jet is ~8 × 108. Our model is energetically capable of producing the observed X-ray emission, even without young stars. We also reproduce the radio through X-ray spectrum of the jet, albeit in a downstream region with distinctly fewer young stars, and recover the mean X-ray spectral index. We derive an internal entrainment rate of ~2.3 × 10-3 M⊙ yr-1 which implies substantial jet deceleration. Our absolute nucleosynthetic yields for the Asymptotic Giant Branch stellar population in the jet show the highest amounts for 4He, 16O, 12C, 14N and 20Ne. If some of the events at ≥55 EeV detected by the Pierre Auger Observatory originate from internal entrainment in Centaurus A, we predict that their composition will be largely intermediate-mass nuclei with 16O, 12C and 14N the key isotopes. [ABSTRACT FROM AUTHOR]

Four VY Scl-type nova-like systems were observed in X-rays during both the low- and the high-optical states. We examined Chandra, ROSAT, Swift and Suzaku archival observations of BZ Cam, MV Lyr, TT Ari and V794 Aql. The X-ray flux of BZ Cam is higher during the low state, but there is no supersoft X-ray source (SSS) as hypothesized in previous articles. No SSS was detected in the low state of the any of the other systems, with the X-ray flux decreasing by a factor between 2 and 50. The best fit to the Swift X-ray spectra is obtained with a multicomponent model of plasma in collisional ionization equilibrium. The high-state high-resolution spectra of TT Ari taken with Chandra Advanced CCD Imaging Spectrometer (ACIS-S) and the Chandra High Energy Transmission Grating (HETG) shows a rich emission line spectrum, with prominent lines of Mg, Si, Ne and S. The complexity of this spectrum seems to have origin in more than one region, or more than one single physical mechanism. While several emission lines are consistent with a cooling flow in an accretion stream, there is at least an additional component. We discuss the origin of this component, which is probably arising in a wind from the system. We also examine the possibility that the VY Scl systems may be intermediate polars, and that while the boundary layer of the accretion disc emits only in the extreme ultraviolet, part of the X-ray flux may be due to magnetically driven accretion. [ABSTRACT FROM PUBLISHER]

We present long-term (months–years) X-ray spectral variability of the Seyfert 1.8 galaxy NGC 1365 as observed by Swift, which provides well-sampled observations over a much longer timescale (six years) and a much larger flux range than is afforded by other observatories. At very low luminosities, the spectrum is very soft, becoming rapidly harder as the luminosity increases and then, above a particular luminosity, softening again. At a given flux level, the scatter in hardness ratio is not very large, meaning that the spectral shape is largely determined by the luminosity. The spectra were therefore summed in luminosity bins and fitted with a variety of models. The best-fitting model consists of two power laws, one unabsorbed and another, more luminous, which is absorbed. In this model, we find a range of intrinsic 0.5–10.0 keV luminosities of approximately 1.1–3.5 erg s−1, and a very large range of absorbing columns, of approximately 1022–1024 cm−2. Interestingly, we find that the absorbing column decreases with increasing luminosity, but that this result is not due to changes in ionization. We suggest that these observations might be interpreted in terms of a wind model in which the launch radius varies as a function of ionizing flux and disc temperature and therefore moves out with increasing accretion rate, i.e. increasing X-ray luminosity. Thus, depending on the inclination angle of the disc relative to the observer, the absorbing column may decrease as the accretion rate goes up. The weaker, unabsorbed, component may be a scattered component from the wind. [ABSTRACT FROM AUTHOR]

The mid-infrared-to-ultraviolet (0.1–10 μm) spectral energy distribution (SED) shapes of 407 X-ray-selected radio-quiet type 1 active galactic nuclei (AGN) in the wide-field ‘Cosmic Evolution Survey’ (COSMOS) have been studied for signs of evolution. For a sub-sample of 200 radio-quiet quasars with black hole mass estimates and host galaxy corrections, we studied their mean SEDs as a function of a broad range of redshift, bolometric luminosity, black hole mass and Eddington ratio, and compared them with the Elvis et al. (E94) type 1 AGN mean SED. We found that the mean SEDs in each bin are closely similar to each other, showing no statistical significant evidence of dependence on any of the analysed parameters. We also measured the SED dispersion as a function of these four parameters, and found no significant dependences. The dispersion of the XMM-COSMOS SEDs is generally larger than E94 SED dispersion in the ultraviolet, which might be due to the broader ‘window function’ for COSMOS quasars, and their X-ray-based selection. [ABSTRACT FROM AUTHOR]

We present the results of the analysis of the X-ray spectrum of the Seyfert 2 Mrk 348, observed by Suzaku and XMM–Newton. The overall spectrum of Mrk 348 can be described by a primary power-law continuum seen through three layers of absorption, of which one is neutral and two are ionized. Comparing Suzaku (2008) and XMM–Newton (2002) observations we find variability of the X-ray spectral curvature. We suggest that the variability can be explained through the change of column density of both the neutral and one of the ionized absorbers, together with a variation of the ionization level of the same absorber. We thus confirm one of the main features presented in past works, where intrinsic column density variability up to ∼1023 cm−2 was observed on time-scales of months. We also find that the photon index of the underlying power-law continuum (Γ ∼ 1.8) is in agreement with the previous observations of this Seyfert 2. [ABSTRACT FROM AUTHOR]

By studying Swift X-ray spectra of an optically selected, non-magnetic sample of nearby cataclysmic variables (CVs), we show that there is a population with X-ray luminosity much lower than accounted for in existing studies. We find an average 0.5–10.0 keV luminosity of $8\times 10^{29}{\,{\rm erg \,s^{-1}}}$ which is an order of magnitude lower than observed in previous samples. Looking at the co-added X-ray spectrum of 20 CVs, we show that the spectral properties of this optically selected, low X-ray luminosity sample – likely characteristic of the dominant population of CVs – resemble that of their brighter counterpart, as well as the X-ray emission originating in the Galactic ridge. It is argued that if the space density of CVs is greater than the current estimates, as it is indeed predicted by population synthesis models, then CVs can significantly contribute to the Galactic ridge emission. [ABSTRACT FROM AUTHOR]

GRS 1915+105 has the largest mass function of any Galactic black hole system, although the error is relatively large. Here we present spectroscopic analysis of medium-resolution infrared Very Large Telescope archival data of GRS 1915+105 in the K band. We find an updated ephemeris, and report on attempts to improve the mass function by a refinement of the radial velocity estimate. We show that the spectra are significantly affected by the presence of phase-dependent CO bandhead emission, possibly originating from the accretion disc: we discuss the impact this has on efforts to better constrain the black hole mass. We report on a possible way to measure the radial velocity utilizing apparent H-band atomic absorption features and also discuss the general uncertainty of the system parameters of this well-studied object. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we present the results from a Suzaku observation of the Galactic supernova remnant G272.2−3.2. The spectra of G272.2−3.2 are well fitted by a single-temperature variable abundance non-equilibrium ionization (VNEI) model with an electron temperature kTe∼ 0.77 keV, an ionization time-scale τ∼ 6.5 × 1010 cm−3 s and an absorbing column density NH∼ 1.1 × 1022 cm−2. We have detected enhanced abundances of Si, S, Ca, Fe and Ni in the centre region, indicating that the X-ray emission has an ejecta origin. We estimate that the electron density is ne∼ 0.48 f−1/2 cm−3, the age is ∼4300 f1/2 yr and the X-ray total mass is Mx= 475 f1/2 M⊙ by taking the distance to be d= 10 kpc. To understand the origin of the centrally peaked X-ray emission of the remnant, we have studied the radial variations of the electron temperature and surface brightness. The relative abundances in the centre region suggest that G272.2−3.2 is the result of a Type Ia supernova explosion. [ABSTRACT FROM AUTHOR]

ABSTRACT We have investigated the environment of the giant radio galaxy NGC 315 with its associated group of galaxies selected by their spectroscopic redshifts. Observations were made with the 2.16-m optical telescope at Xinglong Station of the National Astronomical Observatories of China. In addition to 25 galaxies near NGC 315 with published redshifts, we have successfully determined 21 new redshifts of candidates, five of which are previously unknown members of the NGC 315 galaxy group. We examine and discuss the spatial structure and kinematics of this group (which is part of the Perseus-Pisces filament). Nearly 40 per cent of its members are concentrated near NGC 315, close to the emission from its brighter radio jet. The X-ray luminosity implied by the optical velocity dispersion is higher than that derived empirically from observations of other groups, suggesting that X-ray-emitting gas within the NGC 315 group has a low density. This may be one reason for the size of the radio source. [ABSTRACT FROM AUTHOR]

ABSTRACT Narrow-line Seyfert 1 (NLSy1) galaxies are a peculiar class of type 1 active galactic nuclei (broad-line Seyfert 1 galaxies, hereinafter BLSy1). The X-ray properties of individual objects belonging to this class are often extreme and associated with accretion at high Eddington ratios. Here, we present a study on a sample of 14 NLSy1 galaxies selected at hard X-rays (>20 keV) from the fourth INTEGRAL/IBIS catalogue. The 20-100 keV IBIS spectra show hard-X-ray photon indices flatly distributed (Γ20−100 keV ranging from ∼1.3 to ∼3.6) with an average value of 〈Γ20−100 keV〉= 2.3 ± 0.7, compatible with a sample of hard-X-ray BLSy1 average slopes. Instead, NLSy1 galaxies show steeper spectral indices with respect to BLSy1 galaxies when broad-band spectra are considered. Indeed, we combine XMM-Newton and Swift/XRT with INTEGRAL/IBIS data sets to obtain a wide energy spectral coverage (0.3-100 keV). A constraint on the high energy cut-off and on the reflection component is achieved only in one source, SWIFT J2127.4+5654 ( Ecut-off∼ 50 keV, R= 1.0+0.5− 0.4). Hard-X-ray-selected NLSy1 galaxies do not display particularly strong soft excess emission, while absorption fully or partially covering the continuum is often measured as well as Fe line emission features. Variability is a common trait in this sample, both at X-rays and at hard X-rays. The fraction of NLSy1 galaxies in the hard-X-ray sky is likely to be ∼15 per cent, in agreement with estimates derived in optically selected NLSy1 samples. We confirm the association of NLSy1 galaxies with small black hole masses with a peak at 107 M⊙ in the distribution; however, hard-X-ray NLSy1 galaxies seem to occupy the lower tail of the Eddington ratio distribution of classical NLSy1 galaxies. [ABSTRACT FROM AUTHOR]

Gamma-ray burst (GRB) afterglow 090510 is (so far) the best-monitored afterglow in the optical, X-ray and above 100 MeV, measurements covering two-three decades in time at each frequency. Owing to its power-law temporal decay and power-law spectrum, it seems very likely that the highest energy emission is from the forward shock energizing the ambient medium (the standard blast-wave model for GRB afterglows), the GeV flux and its decay rate being consistent with that model's expectations. However, the synchrotron emission from a collimated outflow (the standard jet model) has difficulties in accounting for the lower energy afterglow emission, where a simultaneous break occurs at 2 ks in the optical and X-ray light curves, but with the optical flux decay (before and after the break) being much slower than in the X-rays (at same time). The measured X-ray and GeV fluxes are incompatible with the higher energy afterglow emission being from same spectral component as the lower energy afterglow emission, which suggests a synchrotron self-Compton model for this afterglow. Cessation of energy injection in the blast wave and an ambient medium with a wind-like density can explain all features of the optical and X-ray light curves of GRB afterglow 090510. Such an ambient medium radial structure is incompatible with this short GRB originating from the merger of two compact stars. [ABSTRACT FROM AUTHOR]

A new serendipitous XMM survey in the area of the Sloan Digital Sky Survey is described ( XMM/SDSS), which includes features such as merging of overlapping fields to increase the sensitivity to faint sources, use of a new parametrization of the XMM point spread function for the source detection and photometry and an accurate estimation of the survey sensitivity. About 40 000 X-ray point sources are detected over a total area of . A subsample of 209 sources detected in the 2-8 keV spectral band with SDSS spectroscopic redshifts in the range of , optical magnitudes mag and (erg s) is selected to explore their distribution on the colour-magnitude diagram. This is compared with the colour-magnitude diagram of X-ray AGN in the AEGIS field at . We find no evidence for evolution of the rest-frame colours of X-ray AGN hosts from to 0.1. This suggests that the dominant accretion mode of the AGN population, which is expected to imprint on the properties of their host galaxies, does not change since . This argues against scenarios that attribute the rapid decline of the accretion power of the Universe with time (1 dex since ) to changes in the AGN fuelling/triggering mode. [ABSTRACT FROM AUTHOR]

We find a self-consistent solution for the outflow rate from an accretion disc around a black hole. The centrifugal pressure dominated shock in a transonic accretion flow can act as a Compton cloud by emitting radiation in the form of hard X-rays. It is also the base of an outflow where considerable matter is ejected. We modify the Rankine-Hugoniot relationship in the accretion flow when the post-shock region suffers energy as well mass-loss. After connecting the post-shock solution in the disc with the sonic surface properties of the outflow, we obtain the ratio of the outflow rate and inflow rate analytically. Our conclusions are (i) the outflow rate is at the most a few per cent of the inflow rate, (ii) the outflow is absent when the shock is relatively weak (more precisely, the compression ratio is less than about 2) and (iii) the outflow rate decreases with the increase of the energy loss at the post-shock region. Thus spectrally soft states will have lesser outflows. [ABSTRACT FROM AUTHOR]

We present the results of spectroscopic, narrow-band and X-ray observations of a 2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of BX/MD galaxies, which are selected to be at by their rest-frame ultraviolet colours, we find that there are five protocluster AGN which have been identified by characteristic emission-lines in their optical/near-IR spectra; this represents an enhancement over the field significant at >98.5 per cent confidence. Using a ∼200-ks Chandra/ACIS-I observation of this field we detect a total of 161 X-ray point sources to a Poissonian false-probability limit of and identify eight of these with BX/MD galaxies. Two of these are spectroscopically confirmed protocluster members and are also classified as emission-line AGN. When compared to a similarly selected field sample, the analysis indicates this is also evidence for an enhancement of X-ray selected BX/MD AGN over the field, significant at >99 per cent confidence. Deep Lyα narrow-band imaging reveals that a total of 4/123 Lyα emitters (LAEs) are found to be associated with X-ray sources, with two of these confirmed protocluster members and one highly likely member. We do not find a significant enhancement of AGN activity in this LAE sample over that of the field (result is significant at only 87 per cent confidence). The X-ray emitting AGN fractions for the BX/MD and LAE samples are found to be and per cent, respectively, for protocluster AGN with at . These findings are similar to results from the protocluster in the SSA 22 field found by Lehmer et al. (2009) , in that both suggest AGN activity is favoured in dense environments at . [ABSTRACT FROM AUTHOR]

The temporal and spectral analysis of nine bright X-ray flares out of a sample of 113 flares observed by Swift reveals that the flare phenomenology is strictly analogous to the prompt γ-ray emission: high-energy flare profiles rise faster, decay faster and peak before the low-energy emission. However, flares and prompt pulses differ in one crucial aspect: flares evolve with time. As time proceeds, flares become wider, with larger peak lag, lower luminosities and softer emission. The flare spectral peak energy evolves to lower values following an exponential decay which tracks the decay of the flare flux. The two flares with best statistics show higher than expected isotropic energy and peak luminosity when compared to the and prompt correlations. is found to correlate with within single flares, giving rise to a time-resolved . Like prompt pulses, flares define a lag–luminosity relation: . The lag–luminosity is proven to be a fundamental law extending ∼5 decades in time and ∼5 decades in energy. Moreover, this is direct evidence that γ-ray burst (GRB) X-ray flares and prompt γ-ray pulses are produced by the same mechanism. Finally we establish a flare–afterglow morphology connection: flares are preferentially detected superimposed to one-break or canonical X-ray afterglows. [ABSTRACT FROM AUTHOR]

We present an updated catalogue of 113 X-ray flares detected by Swift in the ∼33 per cent of the X-ray afterglows of gamma-ray burst (GRB). 43 flares have a measured redshift. For the first time the analysis is performed in four different X-ray energy bands, allowing us to constrain the evolution of the flare temporal properties with energy. We find that flares are narrower at higher energies: their width follows a power-law relation reminiscent of the prompt emission. Flares are asymmetric structures, with a decay time which is twice the rise time on average. Both time-scales linearly evolve with time, giving rise to a constant rise-to-decay ratio: this implies that both time-scales are stretched by the same factor. As a consequence, the flare width linearly evolves with time to larger values: this is a key point that clearly distinguishes the flare from the GRB prompt emission. The flare 0.3–10 keV peak luminosity decreases with time, following a power-law behaviour with large scatter: . When multiple flares are present, a global softening trend is established: each flare is on average softer than the previous one. The 0.3–10 keV isotropic energy distribution is a lognormal peaked at 1051 erg, with a possible excess at low energies. The flare average spectral energy distribution is found to be a power law with spectral energy index . These results confirmed that the flares are tightly linked to the prompt emission. However, after considering various models we conclude that no model is currently able to account for the entire set of observations. [ABSTRACT FROM AUTHOR]

We report a study of the X-ray emission from the nuclear region of the low-surface-brightness (LSB) galaxy UGC 6614. Very little is known about the central objects in LSB galaxies, especially their X-ray properties and X-ray spectra. In this study we have used XMM–Newton archival data to study the characteristics of the X-ray spectrum and the X-ray flux variability of the active galactic nucleus (AGN) in the LSB galaxy UGC 6614. The nucleus of UGC 6614 is very bright in X-ray emission with an absorption-corrected 0.2–10.0 keV luminosity of . The X-ray spectrum is found to be power-law type with a moderate column density. A short time-scale of intensity variation and large X-ray flux are indicative of the presence of a black hole at the centre of this galaxy. Using the method of excess variance, we have determined the black hole mass to be . The X-ray spectral properties are similar to that of the Seyfert I-type AGNs. Our study thus demonstrates that although LSB galaxies are poor in star formation, they may harbour AGNs with X-ray properties comparable to that seen in more luminous spiral galaxies. [ABSTRACT FROM AUTHOR]

In this article, we use simulated and experimental data to explore how three operator-controllable parameters-(1) signal level, (2) detector resolution, and (3) number of factors chosen for analysis-affect quantitative analyses of scanning transmission electron microscopy-energy dispersive X-ray spectroscopy spectrum images processed by principal component analysis (PCA).We find that improvements in both signal level and detector resolution improve the precision of quantitative analyses, but that signal level is the most important. We also find that if the rank of the PCA solution is not chosen properly, it may be possible to improperly fit the underlying data and degrade the accuracy of results. Additionally, precision is degraded in the case when too many factors are included in the model. [ABSTRACT FROM AUTHOR]

A high quality X-ray spectrum image of a 3.3 μm diameter sphere of K411 glass resting on a copper substrate was collected at 25 keV. The same sample configuration was modeled using the NISTMonte Monte Carlo simulation of electron and X-ray transport as is integrated into the quantitative X-ray microanalysis software package DTSA-II. The distribution of measured and simulated X-ray intensity compare favorably for all the major lines present in the spectra. The simulation is further examined to investigate the influence of angle-of-incidence, sample thickness, and sample diameter on the generated and measured X-ray intensity. The distribution of generated X-rays is seen to deviate significantly from a naive model which assumes that the distribution of generated X-rays is similar to bulk within the volume they share in common. It is demonstrated that the angle at which the electron beam strikes the sample has nonnegligible consequences. It is also demonstrated that within the volume that the bulk and particle share in common that electrons, which have exited and later reentered the particle volume, generate a significant fraction of the X-rays. Any general model of X-ray generation in particles must take into account the lateral spread of the scattered electron beam. [ABSTRACT FROM AUTHOR]

We present a general self-consistent lepto/hadronic jet model for the non-thermal electromagnetic emission of microquasars. The model is applied to the low-mass microquasar (LMMQ) GX 339-4 and predicts its high-energy features. We assume that both leptons and hadrons are accelerated up to relativistic energies by diffusive shock acceleration and calculate their contribution to the electromagnetic spectrum through all main radiative processes. The radiative contribution of secondary particles (pions, muons and electron–positron pairs) is included. We use a set of simultaneous observations in radio and X-rays to constrain the model parameters and find the best fit to the data. We obtain different spectral energy distributions that can explain the observations, and make predictions for the high-energy emission. Observations with gamma-ray instruments like Fermi can be used to test the model and determine the proton content of the jets. Finally, we estimate the positron injection in the surrounding medium. Our findings support the suggested association between LMMQs and the observed distribution of the 511 keV line flux observed by INTEGRAL. [ABSTRACT FROM AUTHOR]

We use XMM–Newton and Swift data to study a spectral variability in the ultraluminous X-ray source (ULX), Holmberg IX X−1. The source luminosity varies by a factor of 3–4, giving rise to corresponding spectral changes which are significant, but subtle, and not well tracked by a simple hardness ratio. Instead, we co-add the Swift data in intensity bins and do full spectral fitting with disc plus thermal Comptonization models. All the data are well fitted by a low temperature, optically thick Comptonizing corona, and the variability can be roughly characterized by decreasing temperature and increasing optical depth as the source becomes brighter, as expected if the corona is becoming progressively mass loaded by material blown off the super-Eddington inner disc. This variability behaviour is seen in other ULX which has similar spectra, but is opposite to the trend seen in the ULX with much softer spectra. This supports the idea that there are two distinct physical regimes in ULXs, where the spectra go from being dominated by a disc-corona to being dominated by a wind. [ABSTRACT FROM AUTHOR]

We present the results from the spectral analysis of more than 7500 Rossi X-ray Timing Explorer ( RXTE) spectra of 10 active galactic nuclei (AGN). Our main goal was to study their long-term X-ray spectral variability. The sources in the sample are nearby, X-ray bright, and they have been observed by RXTE regularly over a long period of time (∼7–11 yr). High-frequency breaks have been detected in their power spectra, and these characteristic frequencies imply time-scales of the order of a few days or weeks. Consequently, the RXTE observations we have used most probably sample most of the flux and spectral variations that these objects exhibit. Thus, the RXTE data are ideal for our purpose. Fits to the individual spectra were performed in the 3–20 keV energy band. We modelled the data in a uniform way using simple phenomenological models (a power law with the addition of Gaussian line and/or edge to model the iron Kα emission/absorption features, if needed) to consistently parametrize the shape of the observed X-ray continuum of the sources in the sample. We found that the average spectral slope does not correlate with source luminosity or black hole mass, while it correlates positively with the average accretion rate. We have also determined the (positive) spectral slope–flux relation for each object, over a flux range larger than before. We found that this correlation is similar in all objects, except for NGC 5548 which displays limited spectral variations for its flux variability. We discuss this global spectral slope–flux trend in the light of current models for spectral variability. We consider (i) intrinsic variability, expected, for example, from Comptonization processes, (ii) variability caused by absorption of X-rays by a single absorber whose ionization parameter varies proportionally to the continuum flux variations, (iii) variability resulting from the superposition of a constant reflection component and an intrinsic power law which is variable in flux but constant in shape and (iv) variability resulting from the superposition of a constant reflection component and an intrinsic power law which is variable both in flux and in shape. Our final conclusion is that scenario (iv) provides the best fit to the data of all objects, except for NGC 5548. [ABSTRACT FROM AUTHOR]

A strong hard X-ray luminosity from a blazar flags the presence of a very powerful jet. If the jet power is in turn related to the mass accretion rate, the most luminous, hard X-ray blazars should pinpoint the largest accretion rates, and thus the largest black hole masses. These ideas are confirmed by the Swift satellite observations of the blazar S5 0014+813, at the redshift . Swift detected this source with all its three instruments, from the optical to the hard X-rays. Through the construction of its spectral energy distribution, we are confident that its optical-ultraviolet (UV) emission is thermal in origin. Associating it with the emission of a standard optically thick geometrically thin accretion disc, we find a black hole mass, , radiating at 40 per cent the Eddington value. The derived mass is among the largest ever found. Super-Eddington slim discs or thick discs with the presence of a collimating funnel can in principle reduce the black hole mass estimate, but tend to produce spectra bluer than observed. [ABSTRACT FROM AUTHOR]

Hawkins reported on a class of ‘naked’ active galactic nuclei (AGN) characterized by strong amplitude optical brightness variability and the complete absence of broad emission lines in the optical spectrum. The variability suggests that the nucleus is seen directly, however the absence of broad lines contradicts the simple formulation of Unified Models for AGN. We present the results of quasi-simultaneous spectroscopic observations with XMM–Newton and New Technology Telescope (NTT) (La Silla) of two ‘naked’ AGN. We confirm the ‘naked’ nature of Q2131−427 for which no broad emission line components have been detected in the optical spectrum and its X-ray spectrum shows no signs of intrinsic absorption. The optical and X-ray mismatch in this source cannot be ascribed to a high nuclear dust-to-gas ratio and a Compton-thick nature is ruled out on the basis of the high ratio. The broad-line region (BLR) may be completely absent in this source, possibly as a consequence of its low Eddington ratio. On the other hand, the optical spectrum of Q2130−431 shows Hα and Hβ broad emission line components, revealing the presence of a BLR. A mild X-ray absorption is expected in intermediate type 1.8 Seyfert galaxies like Q2130−431, however we put a very low upper limit on the column density , also the low Balmer decrement suggests that the BLR itself does not suffer from reddening. We propose that in this object the BLR is intrinsically weak, making a case of ‘true’ intermediate Seyfert galaxy. We also report on the X-ray detection of the Abell 3783 galaxy cluster in the XMM–Newton field of view of the Q2131−427 observation. [ABSTRACT FROM AUTHOR]

Spectrum simulation is a useful practical and pedagogical tool. Particularly with complex samples or trace constituents, a simulation can help to understand the limits of the technique and the instrument parameters for the optimal measurement. DTSA-II, software for electron probe microanalysis, provides both easy to use and flexible tools for simulating common and less common sample geometries and materials. Analytical models based on Φ(ρz) curves provide quick simulations of simple samples. Monte Carlo models based on electron and X-ray transport provide more sophisticated models of arbitrarily complex samples. DTSA-II provides a broad range of simulation tools in a framework with many different interchangeable physical models. In addition, DTSA-II provides tools for visualizing, comparing, manipulating, and quantifying simulated and measured spectra. [ABSTRACT FROM AUTHOR]

We present results from a study of short-term variability in 19 archival observations by XMM–Newton of 16 ultraluminous X-ray sources (ULXs). Eight observations (six sources) showed intrinsic variability with power spectra in the form of either a power-law or broken power-law-like continuum and in some cases quasi-periodic oscillations (QPOs). The remaining observations were used to place upper limits on the strength of possible variability hidden within. Seven observations (seven sources) yielded upper limits comparable to, or higher than, the values measured from those observations with detectable variations. These represented the seven faintest sources, all with . In contrast, there are four observations (three sources) that gave upper limits significantly lower than both the values measured from the ULX observations with detectable variations, and the values expected by comparison with luminous Galactic black hole X-ray binaries (BHBs) and active galactic nuclei (AGN) in the observed frequency bandpass (10−3–1 Hz). This is the case irrespective of whether one assumes characteristic frequencies appropriate for a stellar mass or an intermediate mass black hole, and means that in some ULXs the variability is significantly suppressed compared to bright BHBs and AGN. We discuss ways to account for this unusual suppression in terms of both observational and intrinsic effects and whether these solutions are supported by our results. [ABSTRACT FROM AUTHOR]

The X-ray quasi-periodic oscillation (QPO) seen in RE J1034+396 is so far unique amongst active galactic nuclei (AGN). Here, we look at another unique feature of RE J1034+396, namely its huge soft X-ray excess, to see if this is related in any way to the detection of the QPO. We show that all potential models considered for the soft energy excess can fit the 0.3–10 keV X-ray spectrum, but the energy dependence of the rapid variability (which is dominated by the QPO) strongly supports a spectral decomposition where the soft excess is from low-temperature Comptonization of the disc emission and remains mostly constant, while the rapid variability is produced by the power-law tail changing in normalization. The presence of the QPO in the tail rather than in the disc is a common feature in black hole binaries (BHBs), but low-temperature Comptonization of the disc spectrum is not generally seen in these systems. The main exception to this is GRS 1915+105, the only BHB which routinely shows super-Eddington luminosities. We speculate that the super-Eddington accretion rates lead to a change in disc structure, and that this also triggers the X-ray QPO. [ABSTRACT FROM AUTHOR]

We present an analysis of the extreme obscuration variability observed during an XMM–Newton 5-d continuous monitoring of the active galactic nuclei (AGN) in NGC 1365. The source was in a reflection-dominated state in the first ∼1.5 d, then a strong increase in the 7–10 keV emission was observed in ∼10 h, followed by a symmetric decrease. The spectral analysis of the different states clearly shows that this variation is due to an uncovering of the X-ray source. From this observation, we estimate a size of the X-ray source cm, a distance of the obscuring clouds and a density . These values suggest that the X-ray absorption/reflection originates from the broad-line region clouds. This is also supported by the resolved width of the iron narrow emission line, consistent with the width of the broad Hβ line. [ABSTRACT FROM AUTHOR]

In this work, the general purpose Monte Carlo N-particle radiation transport computer code (MCNP-4C) was used for the simulation of X-ray spectra in diagnostic radiology. The electron's path in the target was followed until its energy was reduced to 10 keV. A user-friendly interface named 'diagnostic X-ray spectra by Monte Carlo simulation (DXRaySMCS)' was developed to facilitate the application of MCNP-4C code for diagnostic radiology spectrum prediction. The program provides a user-friendly interface for: (i) modifying the MCNP input file, (ii) launching the MCNP program to simulate electron and photon transport and (iii) processing the MCNP output file to yield a summary of the results (relative photon number per energy bin). In this article, the development and characteristics of DXRaySMCS are outlined. As part of the validation process, output spectra for 46 diagnostic radiology system settings produced by DXRaySMCS were compared with the corresponding IPEM78. Generally, there is a good agreement between the two sets of spectra. No statistically significant differences have been observed between IPEM78 reported spectra and the simulated spectra generated in this study. [ABSTRACT FROM AUTHOR]

We present simultaneous optical and X-ray data from Swift for a sample of radio-loud flat-spectrum quasars selected from the Einstein Medium Sensitivity Survey (EMSS). We present also a complete analysis of Swift and INTEGRAL data on four blazars recently discussed as possibly challenging the trends of the hypothesized ‘blazar spectral sequence’. The spectral energy distributions (SEDs) of all these objects are modelled in terms of a general theoretical scheme, applicable to all blazars, leading to an estimate of the jets’ physical parameters. Our results show that, in the case of the EMSS broad line blazars, X-ray selection does not lead to find sources with synchrotron peaks in the UV/X-ray range, as was the case for X-ray-selected BL Lacs. Instead, for a wide range of radio powers all the sources with broad emission lines show similar SEDs, with synchrotron components peaking below the optical/UV range. The SED models suggest that the associated inverse Compton (IC) emission should peak below the GeV range, but could be detectable in some cases by the Fermi Gamma-ray Space Telescope. Of the remaining four ‘anomalous’ blazars, two highly luminous sources with broad lines, claimed to possibly emit synchrotron X-rays, are shown to be better described with IC models for their X-ray emission. For one source with weak emission lines (a BL Lac object) a synchrotron peak in the soft X-ray range is confirmed, while for the fourth source, exhibiting narrow emission lines typical of narrow-line Seyfert 1 galaxies, no evidence of X-ray emission from a relativistic jet is found. We re-examine the standing and interpretation of the original ‘blazar spectral sequence’ and suggest that the photon ambient, in which the particle acceleration and emission occur, is likely the main factor determining the shape of the blazar SED. A connection between SED shape and jet power/luminosity can however result through the link between the mass and accretion rate of the central black hole and the radiative efficiency of the resulting accretion flow, thus involving at least two parameters. [ABSTRACT FROM AUTHOR]

Starting from a complete sample of type 1 active galactic nuclei (AGN) observed by INTEGRAL in the 20–40 keV band, we have selected a set of eight AGN which can be classified as radio-loud objects according to their 1.4 GHz power density, radio-to-hard X-ray flux density ratio and radio morphology. The sample contains six broad-line radio Galaxies and two candidate ones. Most of the objects in our sample display a double-lobe morphology, both on small and large scales. For all the objects, we present broad-band (1–110 keV) spectral analysis using INTEGRAL observations together with archival XMM–Newton, Chandra, Swift/XRT and Swift/BAT data. We constrain the primary continuum (photon index and cut-off energy), intrinsic absorption and reprocessing features (iron line and reflection) in most of the objects. The sources analysed here show remarkable similarities to radio-quiet type 1 AGN with respect to most of the parameters analysed; we only find marginal evidence for weaker reprocessing features in our objects compared to their radio-quiet counterparts. Similarly, we do not find any correlation between the spectral parameters studied and the source core dominance or radio to 20–100 keV flux density ratios, suggesting that what makes our objects radio loud has no effect on their high-energy characteristics. [ABSTRACT FROM AUTHOR]

Spectral fluence of photoneutrons generated in the head of the radiotherapeutic linac Varian 2100 C/D was measured by means of the Bonner spheres spectrometer whose active detector of thermal neutrons was replaced by a track detector, i.e. a sandwich of four CR-39s with the boron radiator inserted between them. Measurements with different collimator settings showed that the fluence of photoneutrons was higher for the more open collimator. [ABSTRACT FROM AUTHOR]

We report the discovery of variability in the X-ray emission from the Wolf–Rayet type star WR 65. Using archival Chandra data spanning over 5 yr, we detect changes of the X-ray flux by a factor of 3 accompanied by changes in the X-ray spectra. We believe that this X-ray emission originates from wind–wind collision in a massive binary system. The observed changes can be explained by the variations in the emission measure of the hot plasma, and in the different absorption column along the binary orbit. The X-ray spectra of WR 65 display prominent emission features at wavelengths corresponding to the lines of strongly ionized Fe, Ca, Ar, S, Si and Mg. WR 65 is a carbon-rich WC9d star that is a persistent dust maker. This is the first investigation of any X-ray spectrum for a star of this spectral type. There are indications that the dust and the complex geometry of the colliding wind region are pivotal in explaining the X-ray properties of WR 65. [ABSTRACT FROM AUTHOR]

To investigate further the comparison between active galactic nuclei (AGN) and black hole X-ray binaries, we have studied the main X-ray variability properties of the Seyfert 1 galaxy Mrk 335. We put particular emphasis on the X-ray time lags, which is a potentially important diagnostic of physical models. From a 100 ks observation by XMM–Newton, we show that the power spectrum of this source is well fitted by a bending power-law model, and the bend time-scale Tb is precisely at the value predicted by the Tb versus Hβ linewidth relation of McHardy et al. Variations in different energy bands show time-scale-dependent time lags, where higher energy bands lag lower ones. The lag, τ, varies as a function of the Fourier frequency, f, of the variability component in the light curves as at low frequencies, but there is a sharp cut-off in the lags at a frequency close to the bend frequency in the power spectrum. Similar behaviour is seen in black hole X-ray binary systems. The length of the time lags increases continuously with energy separation, in an almost loglinear relation. We show that the lag spectra can be produced by fluctuations propagating through the accretion flow as long as the energy spectrum of the X-ray emitting region hardens towards the centre. [ABSTRACT FROM AUTHOR]

We present a full set of model atmosphere equations for the accretion disc around a supermassive black hole irradiated by a hard X-ray lamp of power-law spectral distribution. Model equations allow for multiple Compton scattering of radiation on free electrons, and for large relative photon–electron energy exchange at the time of scattering. We present spectra in specific intensities integrated over the disc surface. Theoretical outgoing intensity spectra show soft X-ray excess below 1 keV, and distinct Kα and Kβ fluorescent lines of iron. We demonstrate the existence of the Compton Shoulder and claim that it can contribute to the asymmetry and equivalent widths of some observed Fe Kα lines in active galactic nuclei. Our models exhibit the effect of limb-brightening in reflected X-rays. [ABSTRACT FROM AUTHOR]

The X-ray line intensity ratio 3C/3D in Fe xvii is potentially one of the most useful plasma diagnostic line ratios for X-ray astronomy. Based on our recent converged and highly accurate atomic calculations for electron impact excitation of Fe xvii using the fully relativistic close-coupling method, we demonstrate that 3C/3D in Fe xvii is not a constant with respect to electron temperature/energy. The cascade effects (including the excitation and recombination population pumping) on 3C/3D as a function of temperature (for Maxwellian plasmas) or electron beam energy (for some laboratory plasmas) are studied and elaborated. For Maxwellian plasmas prevailing in astrophysical sources under the condition of collisional ionization equilibrium, a new and highly accurate 3C/3D line ratio is reported. The values of 3C/3D reported in this work are 2.66, 2.76, 2.81, 2.88 and 2.94 for electron temperatures of 2, 3, 4, 6 and 10 MK, respectively. The uncertainty in our new line ratio is estimated to be about 5 per cent. These new 3C/3D values are expected to have immediate applications for a wide range of X-ray spectra observed from both point sources as well as extended sources. [ABSTRACT FROM AUTHOR]

We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC 3147. The XMM–Newton spectrum shows that the source is unabsorbed in the X-rays . On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low-equivalent width of the iron Kα line (≃130 eV) and the large ratio between the 2–10 keV and the [O iii] fluxes. It seems therefore inescapable to conclude that NGC 3147 intrinsically lacks the Broad-Line Region, making it the first ‘true’ type 2 Seyfert galaxy. [ABSTRACT FROM AUTHOR]

Extensive spectral observations of η Carinae over the last cycle, and particularly around the 2003.5 low-excitation event, have been obtained. The variability of both narrow and broad lines, when combined with data taken from two earlier cycles, reveal a common and well-defined period. We have combined the cycle lengths derived from the many lines in the optical spectrum with those from broad-band X-rays, optical and near-infrared observations, and obtained a period length of d. Spectroscopic data collected during the last 60 yr yield an average period of d, consistent with the present-day period. The period cannot have changed by more than since 1948. This confirms the previous claims of a true, stable periodicity, and gives strong support to the binary scenario. We have used the disappearance of the narrow component of He i 6678 to define the epoch of the Cycle 11 minimum, . The next event is predicted to occur on 2009 January 11 (±2 d). The dates for the start of the minimum in other spectral features and broad-bands are very close to this date, and have well-determined time-delays from the He i epoch. [ABSTRACT FROM AUTHOR]

The magnetic, chemically peculiar A-star HR 710 (HD 15144, ADS 1849A, AB Cet) has a close companion in a nearly circular orbit. Its 3-d period is unusually short for such stars. The system emits moderately hard X-rays, which likely come from a white dwarf secondary (ADS 1849Ab). The Sr ii spectrum is very strong, and the resonance lines show similar core-nib structure to the stronger Ca K line. We place only loose constraints on a model. There are indications of a lower electron/gas pressure than expected from the star's parallax and brightness. Strong-line profiles and anomalous excitation/ionization indicate significant deviations from traditional models, fixed by and abundances. Weak spectral-line profiles and wavelength shifts probably indicate abundance patches rather than the presence of a secondary (ADS 1849Ab) spectrum. Our UV–Visual Echelle Spectrograph (UVES) spectra are from only one epoch. Additional low-noise, high-resolution spectra are needed. We discuss the spectrum within the context of abundance stratification. [ABSTRACT FROM AUTHOR]

We report on the discovery of the cluster RzCS 052 using a modified red-sequence method, follow up spectroscopy and X-ray imaging. This cluster has a velocity dispersion of 710 ± 150 km s−1, a virial mass of (based on 21 spectroscopically confirmed members) and an X-ray luminosity of (0.68 ± 0.47) × 1044 erg s−1 in the [1–4] keV band. This optically selected cluster appears to be of richness class 3 and to follow the known LX–σ v relation for high-redshift X-ray selected clusters. Using these data, we find that the halo occupation number for this cluster is only marginally consistent with what was expected assuming a self-similar evolution of cluster scaling relations, suggesting perhaps a break of them at z∼ 1. We also rule out a strong galaxy merging activity between and today. Finally, we present a Bayesian approach to measuring cluster velocity dispersions and X-ray luminosities in the presence of a background: we critically reanalyse recent claims for X-ray underluminous clusters using these techniques and find that the clusters can be accommodated within the existing LX–σ v relation. [ABSTRACT FROM AUTHOR]

We present a power spectral analysis of a 100-ks XMM–Newton observation of the Narrow Line Seyfert 1 galaxy Ark 564. When combined with earlier RXTE and ASCA observations, these data produce a power spectrum covering seven decades of frequency which is well described by a power law with two very clear breaks. This shape is unlike the power spectra of almost all other active galactic nuclei (AGN) observed so far, which have only one detected break, and resemble Galactic binary systems in the soft state. The power spectrum can also be well described by the sum of two Lorentzian-shaped components, the one at higher frequencies having a hard spectrum, similar to those seen in Galactic binary systems. Previously we have demonstrated that the lag of the hard-band variations relative to the soft band in Ark 564 is dependent on variability time-scale, as seen in Galactic binary sources. Here we show that the time-scale dependence of the lags can be described well using the same two-Lorentzian model which describes the power spectrum, assuming that each Lorentzian component has a distinct time lag. Thus all X-ray timing evidence points strongly to two discrete, localized, regions as the origin of most of the variability. Similar behaviour is seen in Galactic X-ray binary systems in most states other than the soft state, i.e. in the low-hard and intermediate/very high states. Given the very high accretion rate of Ark 564 the closest analogy is with the very high (intermediate) state rather than the low-hard state. We therefore strengthen the comparison between AGN and Galactic binary sources beyond previous studies by extending it to the previously poorly studied very high accretion rate regime. [ABSTRACT FROM AUTHOR]

Chandra grating spectra of a sample of 15 massive OB stars were analysed under the basic assumption that the X-ray emission is produced in an ensemble of shocks formed in the winds driven by these objects. Shocks develop either as a result of radiation-driven instabilities or due to confinement of the wind by a relatively strong magnetic field, and since they are radiative, a simple model of their X-ray emission was developed that allows a direct comparison with observations. According to our model, the shock structures (clumps, complete or fractional shells) eventually become ‘cold’ clouds in the X-ray sky of the star. As a result, it is expected that for large covering factors of the hot clumps, there is a high probability for X-ray absorption by the ‘cold’ clouds, resulting in blueshifted spectral lines. Our analysis has revealed that such a correlation indeed exists for the considered sample of OB stars. As to the temperature characteristics of the X-ray emission plasma, the studied OB stars fall in two groups: (i) one with plasma temperature limited to ∼0.1–0.4 keV and (ii) the other with X-rays produced in plasmas at considerably higher temperatures. We argue that the two groups correspond to different mechanisms for the origin of X-rays: in radiation-driven instability shocks and in magnetically confined wind shocks, respectively. [ABSTRACT FROM AUTHOR]