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J. Larsson A. C. Fabian G. Miniutti R. R. Ross 《Monthly notices of the Royal Astronomical Society》2007,376(1):348-352
We present a study of the spectral variability of the Seyfert I galaxy MCG–6-30-15 based on the two long XMM–Newton observations from 2000 and 2001. The X–ray spectrum and variability properties of the 2001 data have previously been well described with a two-component model consisting of a variable power-law and a much less variable reflection component, containing a broad relativistic iron line from the accretion disc around a rapidly rotating Kerr black hole. The lack of variability of the reflection component has been interpreted as an effect of strong gravitational light bending very close to the central black hole. Using an improved reflection model, we fit the two-component model to time-resolved spectra of both observations. Assuming that the photon index of the power law is constant, we reconfirm the old result and show that this does not depend on the time-scale of the analysis. 相似文献
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Andreas Fries Rütger Rollenbeck Fabian Bayer Victor Gonzalez Fernando Oñate-Valivieso Thorsten Peters Jörg Bendix 《Meteorology and Atmospheric Physics》2014,126(1-2):13-29
The precise estimation of precipitation quantities in tropical mountain regions is in great demand by ecological and hydrological studies, due to the heterogeneity of the rainfall distribution and the lack of meteorological station data. This study uses radar images and ground station data to provide the required high-resolution precipitation maps. Also wind data are taken into account, due to its influence on the precipitation formation and to demonstrate the relation between synoptic wind, topography and the precipitation distribution inside small mountain valleys. The study analyses the rainfall distribution and amounts of 4 days inside the San Francisco Valley, a small catchment in the tropical Andes of southern Ecuador, representing different seasons and the typical atmospheric flows, which are correlated to the annual precipitation map. The results show that the rainfall distribution and amounts are generally defined by the wind direction and velocity, besides the topographic location in relation to the main barriers and pathways. The dominant wind direction causes a division of the catchment in a wetter eastern and a dryer western part. Moreover, the annual seasons are reversed; the main rainy season for the eastern part occurs between June and August, while the western part reaches the precipitation maximum between January and March. This may have influence on the species composition at the different slopes and the annual hydrological cycle inside the catchment. 相似文献
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M. A. Worsley A. C. Fabian F. E. Bauer D. M. Alexander W. N. Brandt B. D. Lehmer 《Monthly notices of the Royal Astronomical Society》2006,368(4):1735-1741
The emission from individual X-ray sources in the Chandra Deep Fields and XMM – Newton Lockman Hole shows that almost half of the hard X-ray background above 6 keV is unresolved and implies the existence of a missing population of heavily obscured active galactic nuclei (AGN). We have stacked the 0.5–8 keV X-ray emission from optical sources in the Great Observatories Origins Deep Survey (GOODS; which covers the Chandra Deep Fields) to determine whether these galaxies, which are individually undetected in X-rays, are hosting the hypothesized missing AGN. In the 0.5–6 keV energy range, the stacked-source emission corresponds to the remaining 10–20 per cent of the total background – the fraction that has not been resolved by Chandra . The spectrum of the stacked emission is consistent with starburst activity or weak AGN emission. In the 6–8 keV band, we find that upper limits to the stacked X-ray intensity from the GOODS galaxies are consistent with the ∼40 per cent of the total background that remains unresolved, but further selection refinement is required to identify the X-ray sources and confirm their contribution. 相似文献
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Fractional abundances of stratospheric negative ions are for the first time explicitly reported. The measurements made by balloon-borne ion mass spectrometers also rely on recent studies of electric field induced collisional dissociation of negative cluster ions conducted at our laboratory. These indicate that the negative ion composition measurements around 36 km conducted by our group do not suffer from any significant dissociation. The new composition data support ion identifications NO3?(HNO3)b and HSO4?(H2SO4)c(HNO3)d and the underlying ion reactions propo previously. Moreover, it is found that HSO4?(H2SO4)g-ions appear to be particularly stable and that H2SO4-association is very fast. Implications of the ion composition data for ion processes are discussed. 相似文献
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