Particle acceleration and non-thermal emission in the pulsar outer magnetospheric gap     

J. Takata  H.-K. Chang  S. Shibata 《Monthly notices of the Royal Astronomical Society》2008,386(2):748-758

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γ-rays from binary system with energetic pulsar and Be star with aspherical wind: PSR B1259−63/SS2883     

A. Sierpowska-Bartosik  W. Bednarek 《Monthly notices of the Royal Astronomical Society》2008,385(4):2279-2288

At least one massive binary system containing an energetic pulsar, PSR B1259−63/SS2883, has been recently detected in the TeV γ-rays by the HESS telescopes. These γ-rays are likely produced by particles accelerated in the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization of soft radiation from the massive star. However, the process of γ-ray production in such systems can be quite complicated due to the anisotropy of the radiation field, complex structure of the pulsar wind termination shock and possible absorption of produced γ-rays which might initiate leptonic cascades. In this paper, we consider in detail all these effects. We calculate the γ-ray light curves and spectra for different geometries of the binary system PSR B1259−63/SS2883 and compare them with the TeV γ-ray observations. We conclude that the leptonic inverse-Compton model, which takes into account the complex structure of the pulsar wind shock due to the aspherical wind of the massive star, can explain the details of the observed γ-ray light curve.  相似文献   

Jitter radiation in gamma-ray bursts and their afterglows: emission and self-absorption     

Jared C. Workman  Brian J. Morsony  Davide Lazzati  Mikhail V. Medvedev 《Monthly notices of the Royal Astronomical Society》2008,386(1):199-210

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Polarization evolution accompanying the very early sharp decline of gamma-ray burst X-ray afterglows     

Yi-Zhong Fan  Dong Xu  Da-Ming Wei 《Monthly notices of the Royal Astronomical Society》2008,387(1):92-96

In the synchrotron radiation model, the polarization property depends on both the configuration of the magnetic field and the geometry of the visible emitting region. Some peculiar behaviours in the X-ray afterglows of gamma-ray bursts (GRBs) observed with Swift , such as energetic flares and a plateau followed by a sharp drop, might be highly linearly polarized because the outflows powering these behaviours may be dominated by Poynting flux. The breakdown of the symmetry of the visible emitting region may also be well hidden in the peculiar X-ray data and may give rise to interesting polarization signatures. In this paper, we focus on the polarization accompanying the very early sharp decline of GRB X-ray afterglows. We show that strong polarization evolution is possible in both the high latitude emission model and the dying central engine model, which are used to interpret this sharp X-ray decline. It is thus not easy to efficiently probe the physical origin of the very early X-ray sharp decline with future polarimetry. Strong polarization evolution is also possible in the decline phase of X-ray flares and in the shallow decline phase of X-ray light curves characterized by chromatic X-ray versus optical breaks. A detector such as the X-ray Telescope (XRT), but with polarization capability, on board a satellite like Swift would be suitable for testing our predictions.  相似文献   

A New Approach for Estimating Kinetic Luminosity of Jet in AGNs     

Mao-Li Ma Xin-Wu Cao Dong-Rong Jiang Min-Feng Gu 《天体物理学报》2008,8(1):39-49

The Konigl inhomogeneous jet model can successfully reproduce most observational features of jets in active galactic nuclei （AGN）, when suitable physical parameters are adopted. We improve Konigl＇s calculations on the core emission from the jet with a small viewing angle θ0 - φ （φ is half opening angle of the conical jet）. The proper motion of the jet component provides a constraint on the jet kinematics. Based on the inhomogeneous jet model, we use the proper motion data of the jet component to calculate the minimal kinetic luminosity of the jet required to reproduce the core emission measured by the very-long- baseline interferometry （VLBI） for a sample of BL Lac objects. Our results show that the minimal kinetic luminosity is slightly higher than the bolometric luminosity for most sources in the sample, which implies that radiatively inefficient accretion flows （RIAFs） may be in those BL Lac objects, or/and the properties of their broad-line regions （BLRs） are significantly different from flat-spectrum radio-loud quasars.  相似文献   

Time dependent monochromatic scattering of radiation in one dimensional media: Analytical and numerical solutions     

D. I. Nagirner  S. L. Kirusheva 《Astrophysics》2008,51(1):85-98

In order to choose a numerical method for solving the time dependent equations of radiative transport, we obtain an exact solution for the time dependent radiation field in a one dimensional infinite medium with monochromatic, isotropic scattering for sources with an arbitrary spatial distribution and an arbitrary time variation of their power. The Lax-Wendroff method seems to be the most suitable. Because it is assumed that radiation delay is caused by the finite speed of light, the following difficulty arises when the numerical method is used: the region of variation of the variables (position τ and time t) is triangular (the inequality τ ≤ t). This difficulty is overcome by expanding the unknown functions in series in terms of small values of the time and position. By comparing the numerical and exact solutions for a point source with a given time dependence for its power and with pure scattering, the number of steps in the variables required to obtain a desired accuracy is estimated. This numerical method can be used to calculate the intensity and polarization of the radiation from sources in the early universe during epochs close to the recombination epoch. __________ Translated from Astrofizika, Vol. 51, No. 1, pp. 109–123 (February 2008).  相似文献   

Seasonal temperature responses to land-use change in the western United States   总被引：2，自引：0，他引：2  

Lara M. Kueppers  Mark A. Snyder  Lisa C. Sloan  Dan Cayan  Jiming Jin  Hideki Kanamaru  Masao Kanamitsu  Norman L. Miller  Mary Tyree  Hui Du  Bryan Weare 《Global and Planetary Change》2008,60(3-4):250-264

In the western United States, more than 79 000 km² has been converted to irrigated agriculture and urban areas. These changes have the potential to alter surface temperature by modifying the energy budget at the land–atmosphere interface. This study reports the seasonally varying temperature responses of four regional climate models (RCMs) – RSM, RegCM3, MM5-CLM3, and DRCM – to conversion of potential natural vegetation to modern land-cover and land-use over a 1-year period. Three of the RCMs supplemented soil moisture, producing large decreases in the August mean (− 1.4 to − 3.1 °C) and maximum (− 2.9 to − 6.1 °C) 2-m air temperatures where natural vegetation was converted to irrigated agriculture. Conversion to irrigated agriculture also resulted in large increases in relative humidity (9% to 36% absolute change). Modeled changes in the August minimum 2-m air temperature were not as pronounced or consistent across the models. Converting natural vegetation to urban land-cover produced less pronounced temperature effects in all models, with the magnitude of the effect dependent upon the preexisting vegetation type and urban parameterizations. Overall, the RCM results indicate that the temperature impacts of land-use change are most pronounced during the summer months, when surface heating is strongest and differences in surface soil moisture between irrigated land and natural vegetation are largest.  相似文献   

中国世界地质公园格局浅谈及展望   总被引：1，自引：0，他引：1  

吴亮君  朱海燕  陈伟海  容悦冰  莫大桂  容海莲 《地质论评》2019,65(5):1198-1216

联合国教科文组织世界地质公园是一项重要的国际合作机制,借助此机制,中国近15年来申请并建立了39家世界地质公园,成为当前全球世界地质公园最多的国家。文章通过世界地质公园建立以来的一系列相关统计资料,分析中国世界地质公园的类型、岩石构造、分布特征,阶段性地总结当前发展成果与优劣势,并探讨其未来的发展期望。总体上看,中国世界地质公园囊括的地质遗迹类型丰富,源自岩石、构造、化石、水体、冰川等类型的地质遗迹不一而足。依据核心地质遗迹所处地貌特征,可以将中国现有的世界地质公园划分为山麓型、低山型、荒原型、滨海型、湖沼型、洞穴型6个类型。另外,中国世界地质公园分布广泛,64%的省级行政区都建立了世界地质公园,公园涵盖了多种不同的地质、地理、人文历史区域,具有丰富的区域类型。这一系列成绩与我国疆土辽阔、世界级品牌众多、地质公园研究基础深厚、地质与原住民关系度高、国家与地方支持力度大的优势密切相关。但通过不同分区模式进行剖析,也暴露出了公园建设发展不平衡的问题,东部公园远多于西部,人口密度与公园密度较为相关,并且已建成的公园也逐渐出现了一些管理上的问题。针对这些问题,本文分别梳理了根源和影响因素,认为自然条件、经济建设发展速度是对公园当前格局的主要影响因素,并归纳了当前世界地质公园管理上最需要注意的问题。最后,文章针对未来的资源整合与申报,尤其是西部公园申报,提出了四个可能的有利方向。  相似文献   

Heritage stone in South Australia     

B. J. Cooper 《Australian Journal of Earth Sciences》2019,66(6):947-953

South Australia has the greatest utilisation of heritage or building stone in Australia because of its lack of timber resources. Consequently, natural stone was intensively used from the beginning of European colonisation. Building stones in South Australia, notable for their variety given the State’s diverse geology, can be challenging to designate as to their international importance. However, dimension stone in South Australia can also be designated as having national, regional, local or prospective importance. Commonly, stone in South Australia is restricted in use to a specific town, or even a single construction, and has only local significance except where use involves special stone characteristics, unusual stone masonry or use in a building with significant heritage. For instance, the town of Second Valley has a localised use of marble, likely the earliest use (1849) of this rock type in the State. Another example, ‘Adelaide Black Granite’, quarried since 1958, should probably be recognised internationally as a ‘Global Heritage Stone Resource’, as it has had intensive monumental use around Australia, utilisation as cladding in modern buildings, as well as paving and walling in Australia’s National Parliament in Canberra. It has also been exported, notably used for the Australian Embassy in Japan and for a major War Memorial at Le Hamel, France. South Australian slate quarries also provide significant heritage stone. For example, the Willunga Slate quarry south of Adelaide has been sourced for roofing slate and walling since 1840 and is arguably the longest continuous mining operation in Australia; this resource has obvious national significance given a period of quarrying extending to the present, coupled with national distribution of its products. Probably the most widespread stone sourced in South Australia is the surface limestone or calcrete, quarried in the Adelaide area until the 1850s and used for general construction. The stone continues to be used in rural areas. While arguably only of local significance, it could be considered to have national importance because of its extensive use in churches, public building, hotels, houses and simple walling across a vast area of South Australia. Additional research is needed to clarify the heritage status of many building stones used in South Australia.  相似文献   

An active reflector antenna using a laser angle metrology system     

Yong Zhang  Jie Zhang  De-Hua Yang  Guo-Hua Zhou  Ai-Hua Li  Guo-Ping Li 《天体物理学报》2012,(6):713-722

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