Does an orbiting star cause periodic modulation of X-rays from NGC6814?
USING data from the Ginga satellite, Done et al.1 have confirmed an Exosat observation2 of high-amplitude periodic modulation in the X-ray emission from the Seyfert galaxy NGC6814. To within observational errors of ∼1%, the period seems to have remained constant at ∼12,100 seconds between 1985 and 1989. An obvious candidate for the phenomenon underlying the periodicity is the orbital motion of a star or low-mass compact object around the central black hole3. As we show here, the presence of an orbiting star could be verified easily by looking for the effects of Lense–Thirring precession of the orbital plane, caused by the dragging of inertia! frames around a rotating black hole. Precession-induced variations in the waveform and in the phase of the observed periodicity should have a period of between a month and a year. Such variations could account for the different waveforms present in the Ginga and Exosat data sets4, and may be detectable in existing Ginga and future Rosat, OSSE/GRO, and Astro-D data.
Inflation of stars by TeV neutrinos
Irradiation by the mixture of TeV neutrinos and electromagnetic radiation has a strong impact on the structure of low-mass stars. The radii of such stars may be increased by a few orders of magnitude. This effect may have very important consequences for processes in the vicinity of supermassive black holes in Active Galactic Nuclei and some X-ray binary systems.
Characterization of Gallo-Roman roads in northern France using micromorphological methods
Abstract The road network plays an important role in the birth and evolution of town planning and structuring of the landscape. It presents unique and original dynamics that encompass both its status and uses. Whatever their reality in the field, stratigraphic sequences are poorly studied using geoarchaeological methods. To document the formation processes of these road networks, micromorphological analyses were undertaken on a street in a Roman secondary town, Sains-du-Nord, on a road in a Roman civitas capital, Metz Divodurum, and on a lane created in medieval times in Lieusaint. Analyses of the Sains-du-Nord street and the Paille-Maille (Metz) road revealed intense vehicle traffic where traffic-related repairs and traffic layers were differentiated. Analyses of the Lieusaint site, enabled specialists to characterize the processes and layers resulting from vehicle traffic. Pedofeatures linked to passage and traffic presented in this paper, can be used to identify such types of space in other case studies. Finally, results show that the use of thin sections of archaeological layers can reveal not only the surface history, but also the original characteristics of traffic circulation space. The microscopic sequences are presented here as descriptive models of formation processes. The monophasic model appears to be the result of ongoing maintenance attributable to the status or continued use of the street (Sains-du-Nord) or lane (Lieusaint). Polyphasic and polycyclic models reflect rhythmic use and allow reconstruction of traffic levels (Paille-Maille (Metz) road).