The impact of accretion disk winds on the X-ray spectrum of AGN: Part 1 - XSCORT

(abridged) The accretion disk in AGN is expected to produce strong outflows, in particular a UV-line driven wind. Despite providing a good fit to the data, current spectral models of the X-ray spectrum of AGN observed through an accretion disk wind are ad-hoc in their treatment of the properties of the wind material. In order to address these limitations we adopt a numerical computation method that links a series of radiative transfer calculations, incorporating the effect of a global velocity field in a self-consistent manner (XSCORT). We present a series of example spectra from the XSCORT code that allow us to examine the shape of AGN X-ray spectra seen through a wind, for a range of velocity and density distributions, total column densities and initial ionization parameters. These detailed spectral models clearly show considerable complexity and structure that is strongly affected by all these factors. The presence of sharp features in the XSCORT spectra contrasts strongly with both the previous models and with the smooth nature of the observed X-ray spectra of AGN with soft X-ray excesses, demonstrating that accretion disk winds are unlikely to be the origin of this mysterious spectral feature. The most significant parameter affecting the presence of the sharp features in the models is the terminal velocity of the wind. Increasing the terminal velocity of the absorbing material to ~c, and hence dramatically increasing the velocity dispersion across the wind, could potentially remove these features resulting in a spectrum similar to the previous models. Such a fast moving outflow cannot be associated with a radiatively driven accretion disk wind, however the presence of a highly relativistic jet may provide an origin for such material.Comment: 14 pages, 9 figures (colour), Accepted for publication in MNRAS (13th Aug 2007). Several significant changes to the text from v

The x-ray corona and jet of cygnus x-1

Evidence is presented indicating that in the hard state of Cygnus X-1, the coronal mag- netic field might be below equipartition with radiation (suggesting that the corona is not powered by magnetic field dissipation) and that the ion temperature in the corona is significantly lower than what predicted by ADAF like models. It is also shown that the current estimates of the jet power set interesting contraints on the jet velocity (which is at least mildly relativistic), the accretion efficiency (which is large in both spectral states), and the nature of the X-ray emitting region (which is unlikely to be the jet).Comment: 8 pages, 1 figure. Accepted for publication in Journal of Modern Physics D, Proceedings of HEPRO II conference, Buenos Aires, Argentina, October 26-30, 200

Calculations in perturbative QCD and analyses involving scalar mesons

The thesis is split into two independent parts. In part I we discuss the phenomenology of jets in e(^+)e(^-) annihilation at small relative transverse momentum, with a view to testing higher order perturbative QCD (viz. the quark form factor). We phenomenologically extrapolate the quark form factor to cover the whole range in transverse momentum by using the exact 0(αs) cross section in the Parisi-Petronzio prescription (PPP). This then enables us to calculate the transverse momentum distribution of charged hadrons at small transverse momentum; we show that this is a poor way of testing the quark form factor, due to problems in fragmentation. Energy-energy correlations at small angles are found to be a much easier cross section to deal with. However, although the quark form factor is compatible with the data in energy-energy correlations, intrinsic transverse momentum dependence was incorporated in a very naive way, using the smearing function ρ(b) borrowed from Drell-Yan (where it describes hadronic structure). Fragmentation and intrinsic transverse momentum can be incorporated in a more physically meaningful way using the appropriate evolution equations. Erroneous approximations stemming from incorrect kinematic limits and misleading leading logarithms are discussed and corrected. This then allows a calculation of the energy weighted acollinearity of jets using a numerical solution of the evolution equations. Results are obtained in both singlet and non-singlet sectors and shown to be compatible with data at Q=30 Gev. The non-singlet sector is shown to be the dominant one at both Q=30 and at 100 Gev, where predictions are also made for the acollinearity. The effect of intrinsic transverse momentum is found to be much more significant in the evolution equation approach than when using the PPP, although at Q=100 Gev this effect is much lessened. Calculations using two-loop Altarelli-Parisi probabilities are discussed and it is demonstrated that these cannot be relied upon to give an unambiguous description of the data, due to gauge and renormalization scheme dependence. Various forms of the running couplingαs are used, but the data as yet does not show a strong preference for one or another. In part II we are concerned with analyses involving the S* and related scalar mesons. We investigate resonant effects in the isoscalar S wave scattering near the KK̅ threshold using data on ππ and KK̅ production. Various coupled channel parameterizations are considered, and using information from below and above KK̅ threshold, the parameters of the S* and ɛ, resonance effects are determined. The ɛ (1400) is found to be in agreement with an ANL analysis and the S* is compatible with a KK̅ bound state picture. We also study interference effects between the (P wave) φ meson and the underlying (K(^-)K(^+)) S wave in the reaction K(^-)p→(K(^-)K(^+)) ٨ at 4.2 Gev/c. A model independent amplitude analysis of the double multipole moments is performed and we investigate the implications for the KK̅→KK̅ S wave amplitude

Complications of pregnancy and delivery in relation to psychosis in adult life: data from the British perinatal mortality survey sample

Original article can be found at: http://www.pubmedcentral.nih.gov/tocrender.fcgi?iid=137629 Copyright BMJ PublishingTo evaluate whether events occurring at or around the time of birth contribute to the onset of psychotic illness in adult life.Peer reviewe

Eddington Accretion and QSO Emission Lines at z ~ 2

Broad Absorption Line (BAL) QSOs have been suggested to be youthful super-accretors based on their powerful radiatively driven absorbing outflows and often reddened continua. To test this hypothesis, we observed near IR spectra of the H$\beta$ region for 11 bright BAL QSOs at redshift z ~ 2. We measured these and literature spectra for 6 BAL QSOs, 13 radio-loud and 7 radio-quiet non-BAL QSOs. Using the luminosity and H$\beta$ broad line width to derive black hole mass and accretion rate, we find that both BAL and non-BAL QSOs at z ~ 2 tend to have higher $L/L_{Edd}$ than those at low z -- probably a result of selecting the brightest QSOs. However, we find that the high z QSOs, in particular the BAL QSOs, have extremely strong Fe II and very weak [O III], extending the inverse relationship found for low z QSOs. This suggests that, even while radiating near $L_{Edd}$, the BAL QSOs have a more plentiful fuel supply than non-BAL QSOs. Comparison with low z QSOs shows for the first time that the inverse Fe II -- [O III] relationship is indeed related to $L/L_{Edd}$, rather than black hole mass.Comment: 18 pages including 5 figures and 1 table. Accepted by the Astrophysical Journal Letter

X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A Puzzling Disconnectedness

We present optical broadband (B and R) observations of the Seyfert 1 nucleus NGC 3516, obtained at Wise Observatory from March 1997 to March 2002, contemporaneously with X-ray 2-10 keV measurements with RXTE. With these data we increase the temporal baseline of this dataset to 5 years, more than triple to the coverage we have previously presented for this object. Analysis of the new data does not confirm the 100-day lag of X-ray behind optical variations, tentatively reported in our previous work. Indeed, excluding the first year's data, which drive the previous result, there is no significant correlation at any lag between the X-ray and optical bands. We also find no correlation at any lag between optical flux and various X-ray hardness ratios. We conclude that the close relation observed between the bands during the first year of our program was either a fluke, or perhaps the result of the exceptionally bright state of NGC 3516 in 1997, to which it has yet to return. Reviewing the results of published joint X-ray and UV/optical Seyfert monitoring programs, we speculate that there are at least two components or mechanisms contributing to the X-ray continuum emission up to 10 keV: a soft component that is correlated with UV/optical variations on timescales >1 day, and whose presence can be detected when the source is observed at low enough energies (about 1 keV), is unabsorbed, or is in a sufficiently bright phase; and a hard component whose variations are uncorrelated with the UV/optical.Comment: 9 pages, AJ, in pres

Strong constraints on a super-Eddington accretion flow : XMM–Newton observations of an intermediate-mass black hole.

RX J1140.1+0307 is a Narrow Line Seyfert 1 (NLS1) with one of the lowest black hole masses known in an AGN (M ≤ 106 M⊙). We show results from two new XMM–Newton observations, exhibiting soft 2–10 keV spectra, a strong excess at lower energies, and fast X-ray variability which is typical of this class of AGN. The soft excess can be equally well fit using either low-temperature Comptonization or highly smeared, ionized reflection models, but we additionally consider the fast X-ray variability to produce covariance, lag and coherence spectra to show that the low-temperature Comptonization model gives a better description of the break in variability properties between soft and hard X-rays. Both these models require an additional component at the softest energies, as expected from the accretion disc. However, standard disc models cannot connect this to the optical/UV emission from the outer disc unless the mass is underestimated by an order of magnitude. The variable optical and far UV emission instead suggests that L/LEdd ∼ 10 through the outer disc, in which case advection and/or wind losses are required to explain the observed broad-band spectral energy distribution. This implies that the accretion geometry close to the black hole is unlikely to be a flat disc as assumed in the recent X-ray reverberation mapping techniques

Rocks and Hard Places: Exploring Educational Psychologists’ Perspectives on “Off-Rolling” or Illegal Exclusionary Practices in Mainstream Secondary Schools in England

Research being undertaken by the Universities of Exeter and Plymouth is exploring educational psychologists’ knowledge of, and perspectives on, exclusionary practices in schools in England, particularly illegal practices referred to as “off-rolling”. Preliminary findings from the survey element of a mixed methods research project are reported here. The role of business models in the provision of educational psychology services to schools is considered through the conceptual lens of Giroux, Agamben and Ball to highlight ambiguities around the client relationship and to recast individualised ethical dilemmas as systemic features that inhibit direct challenges to school practices relating to inclusion. It is suggested that traded and privatised services risk implicating educational psychologists in schools’ management of the (in)visibility of “off-rolling” and the manufactured legitimacy of varied exclusionary practices

An adaptive-binning method for generating constant-uncertainty/constant-significance light curves with Fermi-LAT data

We present a method enabling the creation of constant-uncertainty/constant-significance light curves with the data of the Fermi-Large Area Telescope (LAT). The adaptive-binning method enables more information to be encapsulated within the light curve than with the fixed-binning method. Although primarily developed for blazar studies, it can be applied to any sources. This method allows the starting and ending times of each interval to be calculated in a simple and quick way during a first step. The reported mean flux and spectral index (assuming the spectrum is a power-law distribution) in the interval are calculated via the standard LAT analysis during a second step. The absence of major caveats associated with this method has been established by means of Monte-Carlo simulations. We present the performance of this method in determining duty cycles as well as power-density spectra relative to the traditional fixed-binning method.Comment: 17 pages, 13 figures, 5 tables. Submitted to A&