I. M. Stewart

The XMM-Newton serendipitous survey: V - The Second XMM-Newton serendipitous source catalogue

Aims. Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods. The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results. The catalogue, the largest ever made at X-ray wavelengths, contains 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources. The catalogue fields cover a sky area of more than 500 deg(2). The non-overlapping sky area is similar to 360 deg(2) (similar to 1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties

A multiple-beam CLEAN for imaging intra-day variable radio sources

The CLEAN algorithm, widely used in radio interferometry for the deconvolution of radio images, performs well only if the raw radio image (dirty image) is, to good approximation, a simple convolution between the instrumental point-spread function (dirty beam) and the true distribution of emission across the sky. An important case in which this approximation breaks down is during frequency synthesis if the observing bandwidth is wide enough for variations in the spectrum of the sky to become significant. The convolution assumption also breaks down, in any situation but snapshot observations, if sources in the field vary significantly in flux density over the duration of the observation. Such time-variation can even be instrumental in nature, for example due to jitter or rotation of the primary beam pattern on the sky during an observation. An algorithm already exists for dealing with the spectral variation encountered in wide-band frequency synthesis interferometry. This algorithm is an extension of CLEAN in which, at each iteration, a set of N “dirty beams” are fitted and subtracted in parallel, instead of just a single dirty beam as in standard CLEAN. In the wide-band algorithm the beams are obtained by expanding a nominal source spectrum in a Taylor series, each term of the series generating one of the beams. In the present paper this algorithm is extended to images which contain sources which vary over both frequency and time. Different expansion schemes (or bases) on the time and frequency axes are compared, and issues such as Gibbs ringing and non-orthogonality are discussed. It is shown that practical considerations make it often desirable to orthogonalize the set of beams before commencing the cleaning. This is easily accomplished via a Gram-Schmidt technique.

Maximum-likelihood detection of sources among Poissonian noise

A maximum likelihood (ML) technique for detecting compact sources in images of the X-ray sky is examined. Such images, in the relatively low exposure regime accessible to present X-ray observatories, exhibit Poissonian noise at background flux levels. A variety of source detection methods are compared via Monte Carlo, and the ML detection method is shown to compare favourably with the optimized-linear-filter (OLF) method when applied to a single image. Where detection proceeds in parallel on several images made in different energy bands, the ML method is shown to have some practical advantages which make it superior to the OLF method. Some criticisms of ML are discussed. Finally, a practical method of estimating the sensitivity of ML detection is presented, and is shown to be also applicable to sliding-box source detection.

Matched filters for source detection in the Poissonian noise regime

A procedure is described for estimating an optimum kernel for the detection by convolution of signals among Poissonian noise. The technique is applied to the detection of X-ray point sources in XMM-Newton data, and is shown to yield an improvement in detection sensitivity of up to 60% over the sliding-box method used in the creation of the 1XMM catalog.

Human research ethics – is construction management research concerned?

Abstract Construction Management Research (CMR) depends upon human beings participating in research, the quality of treatment of participants having direct effect on the quality of their participation, in turn that of the research itself, making treatment of humans and the ethical dilemmas that can ensue an important area of competence for CM (Construction Management) researchers. Does the growing field of CMR demonstrate appropriate concern for human research ethics? Evidence of typical CMR research is taken from the online Cooperative Network for Building Researchers (CNBR), particularly a search for “informed consent” collateral. It was found that there was little concern with human research ethics, which we argue is also evident in the lack of research on this matter in CMR-related literature, or any reference to these matters in the relevant professional and institutional bodies. Reasons as to why this might be are proposed. The consequences of the apparent level of concern are that participants can be exposed to “wrongs”, despite pressures for compliance from institutional ethics boards. However, the discipline of critically evaluating human research approach through a framework of ethical considerations is not only morally correct, at least according to the morality that is concerned for consequences to participants, but is also objectively useful to researchers, improving the reliability and validity of their research and lowering barriers to participation.