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L. Maraschi G. C. Perola A. Treves 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(13):67-70
The possibility of explaining the continuous emission of active galactic nuclei in the frame of a model of spherical accretion onto a massive black hole is discussed. Cool inhomogeneities (T 104°K) within the accretion flow could be responsible for the broad line emission if half of the accreting matter is in the dense phase. A crucial test of this hypothesis is the expected correlation between the ratio of the luminosity in lines to the total luminosity and the hardness of the continuous spectrum. 相似文献
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Space Science Reviews - The possibility of producing γ-rays in a close binary system is examined. First the case of systems containing a young pulsar is discussed. It is shown that high energy... 相似文献
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M. Morini D. Maccagni L. Maraschi D. Molteni E. G. Tanzi A. Treves 《Space Science Reviews》1985,40(3-4):601-606
We have observed the BL Lac object PKS 2155-304 with the EXOSAT observatory and with IUE on 1983 October 31 and November 29. At the same time, optical photometry has been obtained. Variability has been observed both on a time scale of hours during the October 31 observation and on the time scale of one month. During the November 29 observation the source was 2 times brighter than in the previous observation, but no spectral modification is found between the two observations. The source has been also detected in the ME instrument and an energy spectrum has been fitted with a power law. A marginal detection in the ME Xenon counters suggests a flattening of the spectrum in the high energy band. These X-ray data extending over three decades in energy are compared with the simultaneous UV and optical observations. 相似文献
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The binary system AM Herculis = 4U 1814 + 50 gives the first well ascertained example of an X-ray emitting magnetic white dwarf. The orbital period (3.1h) is apparent from X-ray to IR frequencies and in linear and circular polarization. Since the time of the identification of the X-ray source the system has been extensively studied. The observations (which range from 1 MeV to 20 m) are reviewed and compared with the present theory of X-ray emitting white dwarfs. 相似文献
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K. Mukai J. M. Bonnet-Bidaut S. Bowyer P. A. Charles L. Chiappetti J. T. Clarke R. H. D. Corbet J. P. Henry G. J. Hill S. M. Kahn L. Maraschi J. Osborne A. Treves M. van der Klis J. van Paradijs S. D. Vrtilek 《Space Science Reviews》1985,40(1-2):151-155
The AM Her type object E2003+225 was observed with EXOSAT, IUE and ground-based telescopes on 1983 Oct. 12. The brightness of the ultrasoft X-ray component allowed the Objective Grating Spectrometer (OGS) to be used, which gave a model-independent determination of the temperature of the blackbody spectrum. The star was observed again on 1984 July 24 by IUE with simultaneous optical spectrophotometry. The high resolution of this observation revealed complex line profiles, and a systematic velocity much smaller than previously reported. The composite energy distribution is presented. 相似文献
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N. Sartore E. Ripamonti A. Treves R. Turolla 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We study the long term dynamics of isolated neutron stars (NSs) for different initial conditions. From the resulting phase-space distributions, we estimate the fraction of NSs bound to the Milky Way. We also estimate the surface and spatial density of NSs in the solar neighborhood and the mean velocity of NSs in the Galactic disk. Estimates of the sky density of NSs towards specific lines of sight, i.e. the Galactic center and the Magellanic Clouds, are also given. 相似文献
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