On understanding the figures of merit for detection and measurement of x-ray polarization

The prospects for accomplishing X-ray polarization measurements appear to have grown in recent years after a more than 35-year hiatus. Unfortunately, this long hiatus has brought with it some confusion over the statistical uncertainties associated with polarization measurements of astronomical sources. The heart of this confusion stems from a misunderstanding (or potential misunderstanding) of a standard figure of merit-the minimum detectable polarization (MDP)-that one of us introduced many years ago. We review the relevant statistics, and quantify the differences between the MDP and the uncertainty of an actual polarization measurement. We discuss the implications for future missions.Comment: 5 pages, 2 figures, to be presented at SPIE conference 7732 (paper 13), corrected typo

Measuring x-ray polarization in the presence of systematic effects: Known background

The prospects for accomplishing x-ray polarization measurements of astronomical sources have grown in recent years, after a hiatus of more than 37 years. Unfortunately, accompanying this long hiatus has been some confusion over the statistical uncertainties associated with x-ray polarization measurements of these sources. We have initiated a program to perform the detailed calculations that will offer insights into the uncertainties associated with x-ray polarization measurements. Here we describe a mathematical formalism for determining the 1- and 2-parameter errors in the magnitude and position angle of x-ray (linear) polarization in the presence of a (polarized or unpolarized) background. We further review relevant statistics-including clearly distinguishing between the Minimum Detectable Polarization (MDP) and the accuracy of a polarization measurement.Comment: 12 pages, 4 figures, for SPIE conference proceeding

Compound-specific isotope analysis (CSIA) of micropollutants in the environment — current developments and future challenges

Over the last decade, the occurrence of micropollutants in the environment has become a worldwide issue of increasing concern. Compound-specific stable-isotope analysis (CSIA) of natural isotopic abundance may greatly enhance the evaluation of sources and transformation processes of micropollutants, such as pesticides, personal care products or pharmaceuticals. We summarize recent advances from laboratory studies, review current limitations and analytical challenges associated with low concentrations and high polarity of micropollutants, and delineate the potential of micropolluant CSIA for field applications. We highlight future challenges and prospects regarding source apportionment, identification of biotic and abiotic transformation reactions on a mechanistic level, as well as integrative evaluation of degradation hot spots on the catchment scale. Such advances may feed into a framework for risk assessment of micropollutants that includes CSIA

Methods of optimizing X-ray optical prescriptions for wide-field applications

We are working on the development of a method for optimizing wide-field X-ray telescope mirror prescriptions, including polynomial coefficients, mirror shell relative displacements, and (assuming 4 focal plane detectors) detector placement along the optical axis and detector tilt. With our methods, we hope to reduce number of Monte-Carlo ray traces required to search the multi-dimensional design parameter space, and to lessen the complexity of finding the optimum design parameters in that space. Regarding higher order polynomial terms as small perturbations of an underlying Wolter I optic design, we begin by using the results of Monte-Carlo ray traces to devise trial analytic functions, for an individual Wolter I mirror shell, that can be used to represent the spatial resolution on an arbitrary focal surface. We then introduce a notation and tools for Monte-Carlo ray tracing of a polynomial mirror shell prescription which permits the polynomial coefficients to remain symbolic. In principle, given a set of parameters defining the underlying Wolter I optics, a single set of Monte-Carlo ray traces are then sufficient to determine the polymonial coefficients through the solution of a large set of linear equations in the symbolic coefficients. We describe the present status of this development effort.Comment: 14 pages, to be presented at SPIE conference 7732 (paper 93

Triassic to Early Jurassic sandstones in North Victoria Land, Antarctica: Composition, provenance, and diagenesis

Diese Arbeit befasst sich mit mesozoischen kontinentalen Siliziklastika der Victoria Group (Beacon Supergroup) in Nordviktorialand (Antarktis). Diese Ablagerungen sind triassischen bis jurassischen Alters und wurden im Transantarktischen Becken abgelagert. Sie werden in zwei Formationen unterteilt. Die Section Peak Formation im Liegenden wird etwa 200 m mächtig und besteht hauptsächlich aus Sandsteinen, lokal auch aus Konglomeraten, Peliten, Kohlen und Tuffiten. Für eine Liefergebietsanalyse der Section Peak Formation wurden petrographische, chemische, und mineralogische Daten sowie Isotopendaten erfasst und interpretiert. Dadurch können verschiedene Sandstein-Typen mit unterschiedlichen Liefergebieten nachgewiesen werden, die zumeist auf lokale Quellen in Nordviktorialand und benachbarte Regionen zurückzuführen sind. In einigen der Sandstein-Typen lokaler Herkunft manifestiert sich der Einfluss eines magmatischen Bogens entlang der aktiven Plattengrenze von Gondwana. Aufgrund der Beckengeometrie, der petrographischen Zusammensetzung und sedimentologischer Indikatoren kann für diesen Teil des Transantarktischen Beckens eine epikratonische Lage abgeleitet werden. Die hangende Shafer Peak Formation erreicht etwa 50 m und besteht vorwiegend aus tuffitischen Sandsteinen. Für den juvenilen Anteil der Tuffite ist eine (soda?)rhyodacitische Quelle sehr wahrscheinlich. Die zahlreichen felsischen Shards deuten auf distale, ultra-plinianische Ausbrüche hin, die höchstwahrscheinlich im Bereich des magmatischen Bogens an der aktiven Plattengrenze von Gondwana stattfanden. Eine tuffitische Einschaltung in der obersten Section Peak Formation ergab ein U-Pb (SHRIMP) Alter von 188,2 ± 2,2 Millionen Jahren, was erstmals ein eindeutig jurassisches Alter (Pliensbach) der obersten Section Peak Formation und der gesamten Shafer Peak Formation beweist