Point source

Abstract: We present a scheme for random summation of an empirical Green9s function to synthesize ground motions from future large events. This scheme obeys the ω 2 scaling law at all frequencies and produces time histories whose envelopes are realistic. Assuming that the source parameters of the empirical Green9s function are known, one needs only to specify the stress parameter of the target event. In the method, the extended target area is approximated by a point source, whose rupture duration, however, is in accordance with its dimension. Although the method does not account for directivity of the source, tests with Mexican data show a good agreement between observed and synthesized motions. We use this approach to compute expected ground motions in the Valley of Mexico from a hypothetical M 8.2 event in the Guerrero gap.

Abstract: Context. Local-Group galaxies provide access to samples of X-ray source populations of whole galaxies. The XMM-Newton survey of the Small Magellanic Cloud (SMC) completely covers the bar and eastern wing with a 5.6 deg2 area in the (0.2−12.0) keV band. Aims. To characterise the X-ray sources in the SMC field, we created a catalogue of point sources and sources with moderate extent. Sources with high extent (≥40′′) have been presented in a companion paper. Methods. We searched for point sources in the EPIC images using sliding-box and maximum-likelihood techniques and classified the sources using hardness ratios, X-ray variability, and their multi-wavelength properties. Results. The catalogue comprises 3053 unique X-ray sources with a median position uncertainty of 1.3′′ down to a flux limit for point sources of ~10-14 erg cm-2 s-1 in the (0.2−4.5) keV band, corresponding to 5 × 1033 erg s-1 for sources in the SMC. We discuss statistical properties, like the spatial distribution, X-ray colour diagrams, luminosity functions, and time variability. We identified 49 SMC high-mass X-ray binaries (HMXB), four super-soft X-ray sources (SSS), 34 foreground stars, and 72 active galactic nuclei (AGN) behind the SMC. In addition, we found candidates for SMC HMXBs (45) and faint SSSs (8) as well as AGN (2092) and galaxy clusters (13). Conclusions. We present the most up-to-date catalogue of the X-ray source population in the SMC field. In particular, the known population of X-ray binaries is greatly increased. We find that the bright-end slope of the luminosity function of Be/X-ray binaries significantly deviates from the expected universal high-mass X-ray binary luminosity function.

Abstract: The problem is to localise a source of gamma radiation using dose rate measurements taken with a gamma probe at various points in space. A statistical model of dose-rate counts is developed using experimental data recorded in a laboratory. The problem is then studied using the theoretical Cramer-Rao bound (CRB) analysis, which quantifies the accuracy with which it is possible to localise the source and estimate its intensity. Three estimation algorithms are implemented and their performance investigated by simulations. The algorithms are then applied to field trial radiological survey data. The maximum likelihood algorithm performs the best of the considered algorithms.

Abstract: We achieved a continuous, stable, ultrashort pulse hard x-ray point source by focusing 1.8-W, 1-kHz, 50-fs laser pulses onto a novel, 30‐µm-diameter, high-velocity, liquid-metal gallium jet. This target geometry avoids most of the debris problems of solid targets and provides nearly 4π illumination. Photon fluxes of 5×108 photons/s are generated in a two-component spectrum consisting of a broad continuum from 4 to 14 keV and strong Kα and Kβ emission lines at 9.25 and 10.26 keV. This source will find wide use in time-resolved x-ray diffraction studies and other applications.