A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1

We have carried out a high statistics (2 Billion events) search for ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3 and Hercules X-1. Using data taken with the CASA-MIA detector over a five year period (1990-1995), we find no evidence for steady emission from either source at energies above 115 TeV. The derived upper limits on such emission are more than two orders of magnitude lower than earlier claimed detections. We also find no evidence for neutral particle or gamma-ray emission from either source on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of large radio flares. Unless one postulates that these sources were very active earlier and are now dormant, the limits presented here put into question the earlier results, and highlight the difficulties that possible future experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published in Physical Review

For their own good: Recruiting children for research

This article arose from the author's experiences as a researcher exploring children's reactions to their parents' separation. Between 1999 and 2004, the author undertook to find out what a sample of Australian children thought of their abilities to participate in decisions that directly affected them following family breakdown. Before beginning the project, the author was required to obtain ethical approval from the university to which he was attached at that time. He also talked with a number of service providers in Adelaide, where he was based, to request that he receive referrals from them once the research was under way. This article describes the difficulties the author experienced in obtaining ethical approval and subsequently in recruiting children for the research. The article reflects on these difficulties and presents a rationale for considering the participation of children in research about them. Copyright © 2008 SAGE Publications