Revealing the X-ray Variability of AGN with Principal Component Analysis

We analyse a sample of 26 active galactic nuclei with deep XMM-Newton observations, using principal component analysis (PCA) to find model independent spectra of the different variable components. In total, we identify at least 12 qualitatively different patterns of spectral variability, involving several different mechanisms, including five sources which show evidence of variable relativistic reflection (MCG-6-30-15, NGC 4051, 1H 0707-495, NGC 3516 and Mrk 766) and three which show evidence of varying partial covering neutral absorption (NGC 4395, NGC 1365, and NGC 4151). In over half of the sources studied, the variability is dominated by changes in a power law continuum, both in terms of changes in flux and power law index, which could be produced by propagating fluctuations within the corona. Simulations are used to find unique predictions for different physical models, and we then attempt to qualitatively match the results from the simulations to the behaviour observed in the real data. We are able to explain a large proportion of the variability in these sources using simple models of spectral variability, but more complex models may be needed for the remainder. We have begun the process of building up a library of different principal components, so that spectral variability in AGN can quickly be matched to physical processes. We show that PCA can be an extremely powerful tool for distinguishing different patterns of variability in AGN, and that it can be used effectively on the large amounts of high-quality archival data available from the current generation of X-ray telescopes.Comment: 25 pages, 27 figures, accepted to MNRAS. Analysis code available on request to lead author. Edit: Rogue table remove

Investigation of slug mitigation: self-lifting approach in a deepwater oil field

Slug flow is a flow assurance issue that staggers production and, in some cases, 'kills the flow' of the well. Severe slugging, a type of slugging which usually occurs at the base of the riser column, causes large amplitudes in the fluctuation of pressure within the riser column and consequently damages equipment placed topside. An adaptation of a novel concept to slug mitigation: the self-lifting model, is presented. This model presents variations to the internal diameter of the self-lift bypass to produce effective mitigation to severe slugging

Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR

Observational evidence has been accumulating that thermonuclear X-ray bursts ignited on the surface of neutron stars influence the surrounding accretion flow. Here, we exploit the excellent sensitivity of NuSTAR up to 79 keV to analyze the impact of an X-ray burst on the accretion emission of the neutron star LMXB 4U 1608-52. The ~200 s long X-ray burst occurred during a hard X-ray spectral state, and had a peak intensity of ~30-50 per cent of the Eddington limit with no signs of photospheric radius expansion. Spectral analysis suggests that the accretion emission was enhanced up to a factor of ~5 during the X-ray burst. We also applied a linear unsupervised decomposition method, namely non-negative matrix factorization (NMF), to study this X-ray burst. We find that the NMF performs well in characterizing the evolution of the burst emission and is a promising technique to study changes in the underlying accretion emission in more detail than is possible through conventional spectral fitting. For the burst of 4U 1608-52, the NMF suggests a possible softening of the accretion spectrum during the X-ray burst, which could potentially be ascribed to cooling of a corona. Finally, we report a small (~3 per cent) but significant rise in the accretion emission ~0.5 h before the X-ray burst, although it is unclear whether this was related to the X-ray burst ignition.Comment: 10 pages, 10 figures, 1 table, to appear in MNRA

Energy Content of Colliding Plane Waves using Approximate Noether Symmetries

This paper is devoted to study the energy content of colliding plane waves using approximate Noether symmetries. For this purpose, we use approximate Lie symmetry method of Lagrangian for differential equations. We formulate the first-order perturbed Lagrangian for colliding plane electromagnetic and gravitational waves. It is shown that in both cases, there does not existComment: 18 pages, accepted for publication in Brazilian J Physic

Measurement of the electron's electric dipole moment using YbF molecules: methods and data analysis

We recently reported a new measurement of the electron's electric dipole moment using YbF molecules [Nature 473, 493 (2011)]. Here, we give a more detailed description of the methods used to make this measurement, along with a fuller analysis of the data. We show how our methods isolate the electric dipole moment from imperfections in the experiment that might mimic it. We describe the systematic errors that we discovered, and the small corrections that we made to account for these. By making a set of additional measurements with greatly exaggerated experimental imperfections, we find upper bounds on possible uncorrected systematic errors which we use to determine the systematic uncertainty in the measurement. We also calculate the size of some systematic effects that have been important in previous electric dipole moment measurements, such as the motional magnetic field effect and the geometric phase, and show them to be negligibly small in the present experiment. Our result is consistent with an electric dipole moment of zero, so we provide upper bounds to its size at various confidence levels. Finally, we review the prospects for future improvements in the precision of the experiment.Comment: 35 pages, 15 figure

Compensation of B-L charge of matter with relic sneutrinos

We consider massless gauge boson connected to B-L charge with and without compensation to complete the investigation of the gauging of B and L charges. Relic sneutrinos predicted by SUSY and composite models may compensate B-L charge of matter. As a consequence of the possible compensation mechanism we have shown that the available experimental data admit the range of the B-L interaction constant, 10^{-29} < {\alpha}_{B-L} < 10^{-12}, in addition to {\alpha}_{B-L} < 10^{-49} obtained without compensation.Comment: 6 page