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11.
E. Bozzo P. Romano C. Ferrigno P. Esposito V. Mangano 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Supergiant fast X-ray transients are a subclass of high mass X-ray binaries displaying a peculiar and still poorly understood extreme variability in the X-ray domain. These sources undergo short sporadic outbursts (LX∼ 1036–1037 erg s−1), lasting few ks at the most, and spend a large fraction of their time in an intermediate luminosity state at about LX∼ 1033–1034 erg s−1. The sporadic and hardly predictable outbursts of supergiant fast X-ray transients were so far best discovered by large field of view (FOV) coded-mask instruments; their lower luminosity states require, instead, higher sensitivity focusing instruments to be studied in sufficient details. In this contribution, we provide a summary of the current knowledge on supergiant fast X-ray transients and explore the contribution that the new space mission concept LOFT, the Large Observatory for X-ray Timing, will be able to provide in the field of research of these objects. 相似文献
12.
Biagio Forte Massimo Materassi Lucilla Alfonsi Vincenzo Romano Giorgiana De Franceschi Paolo Spalla 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Transionospheric radio signals may experience fluctuations in their amplitude and phase due to irregularity in the spatial electron density distribution, referred to as scintillation. Ionospheric scintillation is responsible for transionospheric signal degradation that can affect the performance of satellite based navigation systems. Usually, the scintillation activity is measured by means of indices such as the normalised standard deviation of the received intensity S4 and the standard deviation of the received phase σ? typically calculated over 1 min of data. Data from a GPS scintillation monitor based on 50 Hz measurements recorded at Dirigibile Italia Station (Ny-Alesund, Svalbard), in the frame of the ISACCO project ( De Franceschi et al., 2006) are used to investigate possible adoption of an alternative parameter for the estimate of phase fluctuations: i.e., the standard deviation of the phase rate of change S?. This parameter is shown to better correlate with S4 being much less detrending dependent than σ?. The couple (S4, S?) should be then considered a more physical proxy of radio scintillation than the couple (S4, σ?). 相似文献