Prompt optical emission from gamma-ray bursts with multiple timescale variability of central engine activities     

Si-Yao Xu  Zhuo Li 《中国天文和天体物理学报》2014,(4):411-422

Complete high-resolution light curves of GRB 080319B observed by Swift present an opportunity for detailed temporal analysis of prompt optical emission. With a two-component distribution of initial Lorentz factors, we simulate the dynamical process of shells being ejected from the central engine in the framework of the in- ternal shock model. The emitted radiations are decomposed into different frequency ranges for a temporal correlation analysis between the light curves in different energy bands. The resulting prompt optical and gamma-ray emissions show similar tempo- ral profiles, with both showing a superposition of a component with slow variability and a component with fast variability, except that the gamma-ray light curve is much more variable than its optical counterpart. The variability in the simulated light curves and the strong correlation with a time lag between the optical and gamma-ray emis- sions are in good agreement with observations of GRB 080319B. Our simulations suggest that the variations seen in the light curves stem from the temporal structure of the shells injected from the central engine of gamma-ray bursts. Future observations with high temporal resolution of prompt optical emission from GRBs, e.g., by UFFO- Pathfinder and SVOM-GWAC, will provide a useful tool for investigating the central engine activity.  相似文献   

翡翠原石的放射性水平研究     

欧阳慧萍  张珠福 《岩石矿物学杂志》2014,33(S2):74-76

为了准确掌握翡翠原石的放射性水平,消除公众对珠宝玉石存在放射性的疑虑,本文选取了3种翡翠原石的10件样品,利用高纯锗型(HPGe)低本底多道γ能谱仪测量了样品中天然放射性核素²²⁶Ra、²³²Th和⁴⁰K的比活度值.结果表明,样品中有关核素的比活度值低于或仅略高于仪器检测限,样品的内照指数(I_Ra)和外照指数(I_γ)均远远低于国家对建筑材料中放射性核素的限量规定,说明翡翠原石的放射性水平很低,与环境的天然本底相当,不存在所谓的放射性危害.  相似文献   

济阳坳陷罗家地区各向异性页岩储层全波场地震响应模拟及分析     

邓馨卉  刘财  郭智奇  刘喜武  刘宇巍 《吉林大学学报(地球科学版)》2018,48(4):1231-1243

济阳坳陷罗家地区页岩储层的固有各向异性及水平层理发育使得储层呈现VTI（vertical transversely isotropy）各向异性,而VTI各向异性背景下垂直裂缝的发育使得储层进一步呈现等效正交各向异性特征。本文以正交各向异性介质作为罗家页岩油储层模型,在岩石物理建模中应用Backus平均理论将测井尺度的VTI各向异性粗化至地震尺度,并利用Schoenberg理论在VTI各向异性背景中引入垂直裂缝,进而得到正交各向异性等效介质模型,同时考虑裂缝尺度和流体填充等因素。之后,应用各向异性反射率法进行全波场地震正演模拟,计算正交各向异性页岩油储层AVAZ（amplitude versus azimuth）响应,通过振幅的方位特征进行储层裂缝识别。计算结果表明,PP波、PSV波和PSH波方位振幅响应各不相同,且方位振幅分布图的拟合形状可反映裂缝的发育方向,为页岩油储层中裂缝的地震识别提供依据。  相似文献   

Efficiency of cosmic ray reflections from an ultrarelativistic shock wave     

J. Bednarz  M. Ostrowski 《Monthly notices of the Royal Astronomical Society》1999,310(1):L11-L13

The process of cosmic ray acceleration up to energies in excess of 10²⁰ eV at relativistic shock waves with large Lorentz factors, Γ≫1, requires ∼Γ² particle energy gains at single reflections from the shock (cf. Gallant & Achterberg). In the present Letter , by applying numerical simulations we address an efficiency problem arising for such models. The actual efficiency of the acceleration process is expected to be substantially lower than the estimates of previous authors.  相似文献   

含金破碎蚀变带地面伽玛能谱特征——以吉林伊通新家地区为例     

马俊孝  李之彤  刘海山  杨森 《地质与资源》1999,8(1):45-48

放射性方法是重要的地球物理勘查方法之一.本文以吉林省中部伊通新家地区为例,讨论了一定地质条件下含金破碎蚀变带的地面伽玛能谱特征和放射性异常组合型式,提供了放射性方法应用于金矿勘查的一个实例  相似文献   

Regional flood frequency analysis using support vector regression in arid and semi-arid regions of Iran     

Ebrahim Sharifi Garmdareh  Seyed Saeid Eslamian 《水文科学杂志》2018,63(3):426-440

Regional flood frequency analysis (RFFA) was carried out on data for 55 hydrometric stations in Namak Lake basin, Iran, for the period 1992–2012. Flood discharge of specific return periods was computed based on the log Pearson Type III distribution, selected as the best regional distribution. Independent variables, including physiographic, meteorological, geological and land-use variables, were derived and, using three strategies – gamma test (GT), GT plus classification and expert opinion – the best input combination was selected. To select the best technique for regionalization, support vector regression (SVR), adaptive neuro-fuzzy inference system (ANFIS), artificial neural network (ANN) and nonlinear regression (NLR) techniques were applied to predict peak flood discharge for 2-, 5-, 10-, 25-, 50- and 100-year return periods. The GT + ANFIS and GT + SVR models gave better performance than the ANN and NLR models in the RFFA. The results of the input variable selection showed that the GT technique improved the model performance.  相似文献   

Identifying large‐scale erosion and deposition processes from airborne gamma radiometrics and digital elevation models in a weathered landscape     

Geoff Pickup  Alan Marks 《地球表面变化过程与地形》2000,25(5):535-557

Patterns of erosion and deposition are difficult to identify and measure at catchment and regional scale but it may be possible to infer their distribution from remote sensing using easily measured surrogate variables. Airborne geophysical surveys provide data on gamma ray emissions from surface and near‐surface material and allow estimation of K, Th and U content. Gamma ray signatures are largely determined by lithology but also change with weathering and with erosion and deposition, and may be used as a partial surrogate for those processes. Comparison of gamma ray signatures with topographic characteristics closely related to sediment transport capacity, downstream sorting of sediments, and the extent of erosion and deposition shows strong linkages. Studies in four small catchments in southeastern Australia indicate that K consistently increases as slopes become steeper while Th and U may either increase or decrease. This suggests the presence of fresh rock rather than weathered material and implies removal of material by erosion, although some patterns may result from systematic changes in lithology across catchments. Analysis by lithology confirms the increase in K with slope in granites, metamorphosed sediments and basalt, and also shows a tendency for U to decrease with slope in the granites and basalt. Gamma ray emissions vary only slightly with catchment area (a surrogate measure of water discharge) suggesting that water erosion is limited or that discharge is not closely related to area. Gamma radiometric profiles down hillslopes, averaged across the full range of gradients, show that, in most cases, radioelements initially decrease, probably reflecting increased weathering, but then increase close to valley floors because of accumulation of fine sediments. Analysis by lithology confirms the increase in radioelements close to valley floors in granites and metamorphosed sediments but the trend is less clear in basalt. Gamma ray profiles down floodplains are variable and indicate the amount of deposition and accumulation of weathered material in valley openings and exposure of bedrock in valley constrictions. Simple erosion and deposition models, based on the conservation of mass equation, and applied to the four catchments, show that all radioelements increase as the potential for deposition increases. They reach a low point in zones of no net erosion or deposition and subsequently increase as erosion becomes more intense and weathered material is lost from slopes. Analysis by lithology largely confirms this pattern. The usefulness of airborne geophysical survey data is limited by flight line spacing with most data being flown at a 200–400 m spacing in Australia. However, general trends in erosion and deposition can still be distinguished and there is capacity for calibrating long‐term erosion and deposition models once better approaches to interpretation of gamma ray data have been developed. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

广西花山航空伽马能谱特征及找矿预测          下载免费PDF全文

林曼曼  董根旺  李海明  王猛  宋洋洋  刘媛媛 《地质找矿论丛》2022,37(3):377-383

广西花山岩体为多期（次）侵位花岗岩体，在岩体内部具有良好的铀成矿地质条件。文章基于航空伽马能谱实测资料，对花山花岗岩体的放射性分布特征进行了研究。研究结果显示，花山岩体整体处于放射性偏高场-高场区域，岩体中心偏南部位的铀含量有明显增高趋势，望高单元的核部和华美单元具有明显的铀迁入特征，F参数高值区分布在望高单元的核部，根据元素的迁移富集规律，圈定出铀矿成矿的有利部位，为扩大华南地区铀矿勘探区域提供了地球物理基础资料。  相似文献   

On the time variability of γ‐ray sources: a numerical analysis of variability indices     

D.F. Torres  M.E. Pessah  G.E. Romero 《Astronomische Nachrichten》2001,322(4):223-227

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On the detection of high‐frequency oscillations in short gamma‐ray bursts     

B.E. Zhilyaev  D. Dubinovska 《Astronomische Nachrichten》2009,330(4):404-410

In this work we present the results of an investigation aimed at a search for an oscillatory phenomenon during short gamma‐ray bursts. The wavelet technique, used for this analysis, is applied to the data from the BATSE 3B catalogue. We have detected oscillations, which periods are found to be in the milliseconds range and their amplitudes up to dozens of percents. A possible scenario for such a phenomenon is the coalescence of stellar‐mass black holes and neutron stars. During the coalescence process the matter orbiting the black hole produces rapid, periodic phenomena. Such system will also emit gravitational waves which cause the orbital radius to decrease and leads to the emission of a chirp of radiation. Estimates lead to a timescale of milliseconds for the coalescence process and oscillation frequencies of hundreds of Hz. The gamma‐ray bursts considered in this paper, show both frequencies and survival times of oscillations close to the mentioned values. A chirp phenomenon is also present. We therefore argue in favor of the black hole – neutron star coalescence as a scenario for the production of short gamma‐ray bursts (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献