Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles

To gain a better understanding of the inner disc region that comprises active galactic nuclei it is necessary to understand the pattern in which the disc is illuminated (the emissivity profile) by X-rays emitted from the continuum source above the black hole (corona). The differences in the emissivity profiles produced by various corona geometries are explored via general relativistic ray tracing simulations. Through the analysis of various parameters of the geometries simulated it is found that emissivity profiles produced by point source and extended geometries such as cylindrical slabs and spheroidal coronae placed on the accretion disc are distinguishable. Profiles produced by point source and conical geometries are not significantly different, requiring an analysis of reflection fraction to differentiate the two geometries. Beamed point and beamed conical sources are also simulated in an effort to model jet-like coronae, though the differences here are most evident in the reflection fraction. For a point source we determine an approximation for the measured reflection fraction with the source height and velocity. Simulating spectra from the emissivity profiles produced by the various geometries produce distinguishable differences. Overall spectral differences between the geometries do not exceed 15 per cent in the most extreme cases. It is found that emissivity profiles can be useful in distinguishing point source and extended geometries given high quality spectral data of extreme, bright sources over long exposure times. In combination with reflection fraction, timing, and spectral analysis we may use emissivity profiles to discern the geometry of the X-ray source.Comment: 15 pages, 12 figures. Accepted for publication in MNRA

A Method for the Measurement of Digitizers’ Absolute Phase Error

A lot of engineering applications, from telecommunications to power systems, require accurate measurement of phase angles. Some of them, like synchrophasor measurement and calibration of instrument transformers with digital output, in order to reach high phase measurement accuracy, require the knowledge of phase error of digitizers. Therefore, in this paper a method for the measurement of digitizers’ absolute phase errors is proposed. It adopts a sinewave and two square waves, that are the digitizer sample clock and a phase reference signal. Combining the measurements of the relative phase differences between the adopted signals it is possible to accurately evaluate the absolute phase error of a digitize

Anomalous relaxation kinetics and charge density wave correlations in underdoped BaPb1-xBixO3

Superconductivity often emerges in proximity of other symmetry-breaking ground states, such as antiferromagnetism or charge-density-wave (CDW) order. However, the subtle inter-relation of these phases remains poorly understood, and in some cases even the existence of short-range correlations for superconducting compositions is uncertain. In such circumstances, ultrafast experiments can provide new insights, by tracking the relaxation kinetics following excitation at frequencies related to the broken symmetry state. Here, we investigate the transient terahertz conductivity of BaPb1-xBixO3 - a material for which superconductivity is adjacent to a competing CDW phase - after optical excitation tuned to the CDW absorption band. In insulating BaBiO3 we observed an increase in conductivity and a subsequent relaxation, which are consistent with quasiparticles injection across a rigid semiconducting gap. In the doped compound BaPb0.72Bi0.28O3 (superconducting below Tc=7K), a similar response was also found immediately above Tc. This observation evidences the presence of a robust gap up to T=40 K, which is presumably associated with short-range CDW correlations. A qualitatively different behaviour was observed in the same material fo T>40 K. Here, the photo-conductivity was dominated by an enhancement in carrier mobility at constant density, suggestive of melting of the CDW correlations rather than excitation across an optical gap. The relaxation displayed a temperature dependent, Arrhenius-like kinetics, suggestive of the crossing of a free-energy barrier between two phases. These results support the existence of short-range CDW correlations above Tc in underdoped BaPb1-xBixO3, and provide new information on the dynamical interplay between superconductivity and charge order.Comment: 19 pages, 4 figure

A SspI PCR-RFLP detecting a silent allele at the goat CSN2 locus

The comparison between the cDNA sequence obtained and the published sequences of the goat CSN2 alleles showed a new single nucleotide polymorphism (SNP) (transition C-T) at the 180th nucleotide of the ninth exon. This mutation, which took place at 124 nt from the polyadenylation site, identifies a silent allele at the CSN2 locus named CSN2 A1. Since the 9th exon C-T transition creates a SspI endonuclease restriction site, the SspI digestion of a PCR product of 360 bp spanning the 9th exon and flanking regions, would allow carriers for the presence of thymine to be identified. The allelic frequency of the CSN2 A1 allele, determined in 170 goats belonging to an undefined genetic type reared in the province of Naples (Italy), was 0.23 It has been observed that the sequences in the 3’ untranslated regions (UTR), proximal to the polyadenylation site, can affect the mechanism of mRNA deadenylation and degradation. Therefore, it is reasonable to hypothesize that the C-T transition might, directly or indirectly, influence the stability of the mRNA and, consequently, the amount of protein produced

Caught in the act: Measuring the changes in the corona that cause the extreme variability of 1H 0707-495

The X-ray spectra of the narrow line Seyfert 1 galaxy, 1H 0707-495, obtained with XMM-Newton, from time periods of varying X-ray luminosity are analysed in the context of understanding the changes to the X-ray emitting corona that lead to the extreme variability seen in the X-ray emission from active galactic nuclei (AGN). The emissivity profile of the accretion disc, illuminated by the X-ray emitting corona, along with previous measurements of reverberation time lags are used to infer the spatial extent of the X-ray source. By fitting a twice-broken power law emissivity profile to the relativistically-broadened iron K fluorescence line, it is inferred that the X-ray emitting corona expands radially, over the plane of the accretion disc, by 25 to 30 per cent as the luminosity increases, contracting again as the luminosity decreases, while increases in the measured reverberation lag as the luminosity increases would require also variation in the vertical extent of the source above the disc. The spectrum of the X-ray continuum is found to soften as the total X-ray luminosity increases and we explore the variation in reflected flux as a function of directly-observed continuum flux. These three observations combined with simple, first-principles models constructed from ray tracing simulations of extended coron self-consistently portray an expanding corona whose average energy density decreases, but with a greater number of scattering particles as the luminosity of this extreme object increases.Comment: 12 pages, 4 figures. Accepted for publication in MNRA

Modelling the Extreme X-ray Spectrum of IRAS 13224-3809

The extreme NLS1 galaxy IRAS 13224-3809 shows significant variability, frequency depended time lags, and strong Fe K line and Fe L features in the long 2011 XMM-Newton observation. In this work we study the spectral properties of IRAS 13224-3809 in detail, and carry out a series of analyses to probe the nature of the source, focusing in particular on the spectral variability exhibited. The RGS spectrum shows no obvious signatures of absorption by partially ionised material (warm absorbers). We fit the 0.3-10.0 keV spectra with a model that includes relativistic reflection from the inner accretion disc, a standard powerlaw AGN continuum, and a low-temperature (~0.1 keV) blackbody, which may originate in the accretion disc, either as direct or reprocessed thermal emission. We find that the reflection model explains the time-averaged spectrum well, and we also undertake flux-resolved and time-resolved spectral analyses, which provide evidence of gravitational light-bending effects. Additionally, the temperature and flux of the blackbody component are found to follow the $L\propto T^{4}$ relation expected for simple thermal blackbody emission from a constant emitting area, indicating a physical origin for this component.Comment: 12 pages, 7 figures, accepted for publication in MNRA

Begleitung schwer kranker und sterbender Kinder: Empfehlungen für die Praxis

Zusammenfassung: Der Tod eines Kindes ist bei uns ein seltenes, aber umso erschütternderes Ereignis. Die Begleitung sterbender Kinder ist nur mit Einbezug ihres sozialen Umfeldes möglich und erfordert entwicklungspsychologische Kenntnisse. Der Text fasst Aspekte der Entstehung des kindlichen Todeskonzeptes zusammen und beschreibt die psychischen Reaktionen schwer kranker Kinder und Jugendlicher. Abschließend geben die Autoren, ausgehend von ihren praktischen Erfahrungen, Empfehlungen und Orientierungshilfen für die Sterbebegleitun

An intense soft-excess and evidence for light bending in the luminous narrow-line quasar PHL 1092

The narrow-line quasar PHL 1092 was observed by XMM-Newton at two epochs separated by nearly thirty months. Timing analyses confirm the extreme variability observed during previous X-ray missions. A measurement of the radiative efficiency is in excess of what is expected from a Schwarzschild black hole. In addition to the rapid X-ray variability, the short UV light curves (< 4 hours) obtained with the Optical Monitor may also show fluctuations, albeit at much lower amplitude than the X-rays. In general, the extreme variability is impressive considering that the broad-band (0.4-10 keV rest-frame) luminosity of the source is ~10^45 erg/s. During at least one of the observations, the X-ray and UV light curves show common trends, although given the short duration of the OM observations, and low significance of the UV light curves it is difficult to comment on the importance of this possible correlation. Interestingly, the high-energy photons (> 2 keV) do not appear highly variable. The X-ray spectrum resembles that of many narrow-line Seyfert 1 type galaxies: an intense soft-excess modelled with a multi-colour disc blackbody, a power-law component, and an absorption line at ~1.4 keV. The ~1.4 keV feature is curious given that it was not detected in previous observations, and its presence could be related to the strength of the soft-excess. Of further interest is curvature in the spectrum above ~2 keV which can be described by a strong reflection component. The strong reflection component, lack of high-energy temporal variability, and extreme radiative efficiency measurements can be understood if we consider gravitational light bending effects close to a maximally rotating black hole.Comment: To appear in MNRAS. Submitted March 01, 2004. 9 page

Double dynamical regime of confined water

The Van Hove self correlation function of water confined in a silica pore is calculated from Molecular Dynamics trajectories upon supercooling. At long time in the $\alpha$ relaxation region we found that the behaviour of the real space time dependent correlators can be decomposed in a very slow, almost frozen, dynamics due to the bound water close to the substrate and a faster dynamics of the free water which resides far from the confining surface. For free water we confirm the evidences of an approach to a crossover mode coupling transition, previously found in Q space. In the short time region we found that the two dynamical regimes are overimposed and cannot be distinguished. This shows that the interplay between the slower and the faster dynamics emerges in going from early times to the $\alpha$ relaxation region, where a layer analysis of the dynamical properties can be performed.Comment: 6 pages with 9 figures. RevTeX. Accepted for pulbication in J. Phys. Cond. Mat