PDS 456: an extreme accretion rate quasar?

We present quasi-simultaneous ASCA and RXTE observations of the most luminous known active galactic nucleus in the local ( z <0.3) Universe, the recently discovered quasar PDS 456. Multiwavelength observations have been conducted that show that PDS 456 has a bolometric luminosity of ∼10⁴⁷ erg s⁻¹ peaking in the ultraviolet part of the spectrum. In the X-ray band the 2–10 keV (rest-frame) luminosity is 10⁴⁵ erg s⁻¹. The broad-band X-ray spectrum obtained with ASCA and RXTE contains considerable complexity. The most striking feature observed is a very deep, ionized iron K edge, observed at 8.7 keV in the quasar rest-frame. We find that these features are consistent with reprocessing from highly ionized matter, probably the inner accretion disc. PDS 456 appeared to show a strong (factor of ∼2.1) outburst in just ∼17 ks, although non-intrinsic sources cannot be completely ruled out. If confirmed, this would be an unusual event for such a high-luminosity source, with a light-crossing-time corresponding to ∼2 R _S . The implication would be that flaring occurs within the very central regions, or else that PDS 456 is a 'super-Eddington' or relativistically beamed system. Overall we conclude on the basis of the extreme blue/UV luminosity, the rapid X-ray variability and from the imprint of highly ionized material on the X-ray spectrum, that PDS 456 is a quasar with an unusually high accretion rate.     

Making ends meet in Gondwana: retracing the transforms of the Indian Ocean and reconnecting continental shear zones

Interpretation of the detailed patterns of ocean-floor transforms revealed by satellite altimetry enables the creation of the Indian Ocean to be described quantitatively as four consecutive plate-tectonic regimes separated at 200, 136, 89 and 43 Ma. Each regime is reversed in turn by keeping transform termini coincident and colinear until conjugate points on the margins of pre-existing plates regain their pre-regime integrity. Progressive elimination of the Indian Ocean, demonstrable as a smooth computer animation ( http://www.kartoweb.itc.nl/gondwana ), leads to a refined re-assembly of the continental fragments of central Gondwana that is substantiated by new geological data. A sequence of Euler interval poles that describes the dispersal of the Gondwana fragments, time-calibrated against available magnetic anomaly data, is given. The model requires a mid-Cretaceous position for India's southern tip about 1000 km south of Madagascar, prior to India's rapid northward migration.     

A Semi‐Structured MODFLOW‐USG Model to Evaluate Local Water Sources to Wells for Decision Support

In order to better represent the configuration of the stream network and simulate local groundwater‐surface water interactions, a version of MODFLOW with refined spacing in the topmost layer was applied to a Lake Michigan Basin (LMB) regional groundwater‐flow model developed by the U.S. Geological. Regional MODFLOW models commonly use coarse grids over large areas; this coarse spacing precludes model application to local management issues (e.g., surface‐water depletion by wells) without recourse to labor‐intensive inset models. Implementation of an unstructured formulation within the MODFLOW framework (MODFLOW‐USG) allows application of regional models to address local problems. A “semi‐structured” approach (uniform lateral spacing within layers, different lateral spacing among layers) was tested using the LMB regional model. The parent 20‐layer model with uniform 5000‐foot (1524‐m) lateral spacing was converted to 4 layers with 500‐foot (152‐m) spacing in the top glacial (Quaternary) layer, where surface water features are located, overlying coarser resolution layers representing deeper deposits. This semi‐structured version of the LMB model reproduces regional flow conditions, whereas the finer resolution in the top layer improves the accuracy of the simulated response of surface water to shallow wells. One application of the semi‐structured LMB model is to provide statistical measures of the correlation between modeled inputs and the simulated amount of water that wells derive from local surface water. The relations identified in this paper serve as the basis for metamodels to predict (with uncertainty) surface‐water depletion in response to shallow pumping within and potentially beyond the modeled area, see Fienen et al. (2015a).     

XMM-EPIC observation of MCG–6-30-15: direct evidence for the extraction of energy from a spinning black hole?

We present XMM-Newton European Photon Imaging Camera (EPIC) observations of the bright Seyfert 1 galaxy MCG–6-30-15, focusing on the broad Fe K α line at ∼6 keV and the associated reflection continuum, which is believed to originate from the inner accretion disc. We find these reflection features to be extremely broad and redshifted, indicating an origin in the very central regions of the accretion disc. It seems likely that we have caught this source in the 'deep minimum' state first observed by Iwasawa et al. The implied central concentration of X-ray illumination is difficult to understand in any pure accretion disc model. We suggest that we are witnessing the extraction and dissipation of rotational energy from a spinning black hole by magnetic fields connecting the black hole or plunging region to the disc.     

Distributed velocity method of solving the convective-dispersion equation: 1. Introduction,mathematical theory,and numerical implementation

This is the first part of a two-part paper presenting a new method for treating convective-dispersive transport. The motivation for developing this technique arises from the demands of performing a risk assessment for a nuclear waste repository. These demands include computational efficiency over a relatively large range of Peclet numbers, the ability to handle chains of decaying radionuclides with rather extreme contrasts in both solution velocities and half lives, and the ability to treat leach- or solubility-limited sources. To the extent it has been tested to date, the distributed velocity method (DVM) appears to satisfy these demands. This part contains an overall introduction and presents the mathematical theory, numerical implementation, and example results.     

Measurements in the solar spectrum between 1400 and 1875 Å with a rocket-borne spectrometer

Intensity measurements in the solar continuum throughout the wavelength range 1400 Å–1875 Å are reported for a rocket flight from White Sands, New Mexico at 16:31 h UT on September 24, 1968. These intensities are approximately a factor of 3 lower than other published estimates and suggest a solar temperature minimum of 4400 K or lower which is in agreement with infrared observations.     

COSMOGENIC RADIONUCLIDES AND NOBLE GASES IN THE WETHERSFIELD (1982) CHONDRITE

The Wethersfield (1982) chondrite was assayed for a suite of cosmogenic radionuclides shortly after fall. Data are reported for ⁷Be, ²²Na, ²⁶Al, ⁴⁶Sc, ⁴⁸V, ⁵¹Cr, ⁵⁴Mn, ⁵⁶Co, ⁵⁷Co, and ⁶⁰Co. A comparison is made with predicted results based on a scaling to the Deep River Neutron Monitor. Noble gases were also assayed in a sub-sample. The cosmic ray exposure age is estimated to be 45 million years.     

The potential of mid- and near-infrared diffuse reflectance spectroscopy for determining major- and trace-element concentrations in soils from a geochemical survey of North America

In 2004, soils were collected at 220 sites along two transects across the USA and Canada as a pilot study for a planned soil geochemical survey of North America (North American Soil Geochemical Landscapes Project). The objective of the current study was to examine the potential of diffuse reflectance (DR) Fourier Transform (FT) mid-infrared (mid-IR) and near-infrared (NIRS) spectroscopy to reduce the need for conventional analysis for the determination of major and trace elements in such continental-scale surveys. Soil samples (n = 720) were collected from two transects (east–west across the USA, and north–south from Manitoba, Canada to El Paso, Texas (USA), n = 453 and 267, respectively). The samples came from 19 USA states and the province of Manitoba in Canada. They represented 31 types of land use (e.g., national forest, rangeland, etc.), and 123 different land covers (e.g., soybeans, oak forest, etc.). The samples represented a combination of depth-based sampling (0–5 cm) and horizon-based sampling (O, A and C horizons) with 123 different depths identified. The set was very diverse with few samples similar in land use, land cover, etc. All samples were analyzed by conventional means for the near-total concentration of 49 analytes (C_total, C_carbonate and C_organic, and 46 major and trace elements). Spectra were obtained using dried, ground samples using a Digilab FTS-7000 FT spectrometer in the mid- (4000–400 cm⁻¹) and near-infrared (10,000–4000 cm⁻¹) at 4 cm⁻¹ resolution (64 co-added scans per spectrum) using a Pike AutoDIFF DR autosampler. Partial least squares calibrations were develop using: (1) all samples as a calibration set; (2) samples evenly divided into calibration and validation sets based on spectral diversity; and (3) samples divided to have matching analyte concentrations in calibration and validation sets. In general, results supported the conclusion that neither mid-IR nor NIRS would be particularly useful in reducing the need for conventional analysis of soils from this continental-scale geochemical survey. The extreme sample diversity, likely caused by the widely varied parent material, land use at the site of collection (e.g., grazing, recreation, agriculture, etc.), and climate resulted in poor calibrations even for C_total, C_organic and C_carbonate. The results indicated potential for mid-IR and NIRS to differentiate soils containing high concentrations (>100 mg/kg) of some metals (e.g., Co, Cr, Ni) from low-level samples (<50 mg/kg). However, because of the small number of high-level samples, it is possible that differentiation was based on factors other than metal concentration. Results for Mg and Sr were good, but results for other metals examined were fair to poor, at best. In essence, it appears that the great variation in chemical and physical properties seen in soils from this continental-scale survey resulted in each sample being virtually unique. Thus, suitable spectroscopic calibrations were generally not possible.