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I. A. Grenier M. M. Kaufman Bernadó G. E. Romero 《Astrophysics and Space Science》2005,297(1-4):109-118
A subset of the unidentified EGRET γ-ray sources with no active galactic nucleus or other conspicuous counterpart appears
to be concentrated at medium latitudes. Their long-term variability and their spatial distribution indicate that they are
distinct from the more persistent sources associated with the nearby Gould Belt. They exhibit a large scale height of 1.3
± 0.6 kpc above the Galactic plane. Potential counterparts for these sources include microquasars accreting from a low-mass
star and spewing a continuous jet. Detailed calculations have been performed of the jet inverse Compton emission in the radiation
fields from the star, the accretion disc, and a hot corona. Different jet Lorentz factors, powers, and aspect angles have
been explored. The up-scattered emission from the corona predominates below 100 MeV whereas the disc and stellar contributions
are preponderant at higher energies for moderate (∼15∘) and small (∼1∘) aspect angles, respectively. Yet, unlike in the high-mass, brighter versions of these systems, the external Compton emission
largely fails to produce the luminosities required for 5 to 10 kpc distant EGRET sources. Synchrotron-self-Compton emission
appears as a promising alternative. 相似文献
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Rosa María Mateos Pablo Ezquerro Jose Miguel Azañón Bernadí Gelabert Gerardo Herrera Jose Antonio Fernández-Merodo Daniele Spizzichino Roberto Sarro Inmaculada García-Moreno Marta Béjar-Pizarro 《Landslides》2018,15(4):797-809
The Bàlitx area is located on the steep coastal side of the Tramuntana Range (Majorca), a mountainous region which was declared a World Heritage Site by UNESCO in 2011 in the cultural landscape category. The Bàlitx site was occupied by farming areas with dry stone constructions and water storing systems of both Roman and Islamic origin. The coastal landscape is characterised by a large fault escarpment of up to 260 m in height. Lateral spreading processes are favoured by local stratigraphy and tectonics in an energetic coastal dynamics scenario. Block spreading morphologies are identified along the escarpment, with large, rocky blocks of volumes up to 60?×?103 m3 moving very slowly until their collapse. Consequently, a thick and highly karstified breccia deposit is accumulated at the base of the scarp. The lowest, oldest breccia outcrop has been dated (Th/U), and an age of 82.5?±?5.6 kyr was obtained, reflecting the time span this process has been active. Additionally, numerous geomorphological slope features are identified in the area: landslides, rockfalls, and, more specifically, long and deep cracks in the hanging wall block of the fault, which also reveal active lateral spreading processes. Coastal dynamics have been investigated by interpreting offshore geophysical studies, bathymetry data and borehole information to determine the role of wave energy in the stability of the slope. Additionally, 14 SAR images from the ALOS PALSAR satellite have been exploited for the present work, covering a period spanning from 2007 to 2010, an anomalous rainy period in the region. Images were processed using the Persistent Scattered Interferometry (PSI) technique. PSInSAR results reveal that the rate of movement for the Bàlitx lateral spreading is extremely low (??5.2 mm/year on average), but major activity has been detected in the NE sector, where velocity rates can reach values of up to ??16 mm/year Coastal dynamics in the area can explain this, as a small island generates wave refraction and reflection determining more intense erosive processes in the NE part, which lead to a greater destabilising effect on the slopes. A simple vulnerability approach has been developed to take the elements of cultural heritage into account. Vulnerability increases from SW to NE, in accordance with landslide activity. The Bàlitx case study could provide a testimony to the effects of mass movements and coastal dynamics in an exceptional example of Mediterranean agricultural landscape. 相似文献
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