RE J1034+396: the origin of the soft X-ray excess and quasi-periodic oscillation

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.     

Stable nickel isotopes and cosmogenic beryllium-10 and aluminum-26 in metallic spheroids from Meteor Crater,Arizona

Abstract— The isotopic abundances of Ni in 17 metallic spheroids from Meteor Crater, Arizona, were determined by inductively coupled plasma mass spectrometry (ICP-MS). Sixteen spheroids have normal isotopic abundances. A 17th shows a marginally detectable mass fractionation of 0.40 ± 0.14 %/AMU in favor of the heavier isotopes. The general absence of mass fractionation indicates that open system evaporation caused little loss of Ni. Variable activities of the cosmogenic radionuclides ¹⁰Be and ²⁶Al were measured by accelerator mass spectrometry in separate suites of spheroids. Activities of ²⁶Al in most samples and of ¹⁰Be in metal cores separated from spheroids indicate that they either (1) come from greater depths in the parent meteoroid than do hand specimens, or (2) lost Al and Be during the process of spheroid formation. One individual spheroid has ¹⁰Be and ²⁶Al activities comparable to those of bulk specimens. This result suggests that spheroid formation may occasionally include material from the outermost meter or so of the impactor. Relatively high activities of ¹⁰Be, ～3 dpm/kg, in the siliceous shells of Canyon Diablo spheroids very likely have a meteoric origin.     

Treasure!

The word ‘treasure’ conjures an image of objects of silver and gold, perhaps encrusted with gemstones, and some treasures dug from the ground certainly match this image (Fig. 1 ). However, a theme that ran through the recent exhibition of Treasure at the British Museum was that the archaeological value of treasure does not depend only on its content of precious metals or gems. Many items recovered from archaeological sites are made from or include natural rocks, minerals and gemstones, so that geological and mineralogical techniques and interpretative approaches often make an essential contribution to their study. This article explores the role of scientific examination in realizing the full archaeological value of treasure.

Figure 1 Open in figure viewer PowerPoint Group of items from a Roman hoard, found at Thetford. These objects are not in Treasure but may be seen in Gallery 49 of the British Museum.     

Unification Of Non-Dimensional Solutions To Asymptotic Equations For Plumes Of Different Shape

A model of buoyant fluid rise is developed in aLagrangian framework. Results from the model arevalidated by comparison with laboratory and fieldexperiments. The model is sufficiently general toinclude geometries of any cross-sectional shape. Exact solutions to the asymptotic equations forcontinuous discharges from line and point sources andfor an instantaneous discharge from a point source areconsidered. Prismatic, cylindrical andspherical shapes approximate these three geometries,respectively. Accommodation of these shapes withinthe same general model allows for direct comparison. It is shown that, for discharges into a cross-flowthat may be stratified or unstratified, thenon-dimensional trajectory, thickness and dilution canbe uniquely specified using three parameters. Theseare the non-dimensional size of the source, therelative importance of the initial fluxes of momentumand buoyancy and the number of orthogonal axes throughwhich entrainment can occur. Such non-dimensionalresults are particularly useful for examining thosescenarios for which there are limited experimentaldata.     

The rise of forced plumes in a stably stratified crossflow

Solutions are found describing the rise of turbulent buoyant plumes in a neutral or stably stratified crossflow from a source having finite fluxes of buoyancy, momentum and volume. Plumes from such sources are known as forced plumes. The solutions arise from a unified theory having one disposable parameter, the entrainment constant, and they describe a wide range of behaviour of plumes and jets in a crossflow. Solutions for buoyant plumes indicate that, for any given source, heights of rise are reduced with increased crossflow velocity and increased stratification while for constant environmental parameters, heights of rise are increased with increased fluxes of source buoyancy and momentum and are decreased with source radius. Maximum dilutions occur in plumes from small sources with relatively large buoyancy fluxes in light crossflows with small stratification.