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The High Energy Stereoscopic System (H.E.S.S.) is a system of Imaging Atmospheric Cherenkov Telescopes (IACTs) located in the Khomas Highland in Namibia. It measures cosmic gamma rays of very high energies (VHE; >100 GeV) using the Earth’s atmosphere as a calorimeter. The H.E.S.S. Array entered Phase II in September 2012 with the inauguration of a fifth telescope that is larger and more complex than the other four. This paper will give an overview of the current H.E.S.S. central data acquisition (DAQ) system with particular emphasis on the upgrades made to integrate the fifth telescope into the array. At first, the various requirements for the central DAQ are discussed then the general design principles employed to fulfil these requirements are described. Finally, the performance, stability and reliability of the H.E.S.S. central DAQ are presented. One of the major accomplishments is that less than 0.8% of observation time has been lost due to central DAQ problems since 2009. 相似文献
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We describe the science motivation and development of a pair production telescope for medium-energy (∼5–200 MeV) gamma-ray polarimetry. Our instrument concept, the Advanced Energetic Pair Telescope (AdEPT), takes advantage of the Three-Dimensional Track Imager, a low-density gaseous time projection chamber, to achieve angular resolution within a factor of two of the pair production kinematics limit (∼0.6° at 70 MeV), continuum sensitivity comparable with the Fermi-LAT front detector (<3 × 10−6 MeV cm−2 s−1 at 70 MeV), and minimum detectable polarization less than 10% for a 10 mCrab source in 106 s. 相似文献
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Supernova remnants (SNRs) are among the most important targets for γ-ray observatories. Being prominent non-thermal sources, they are very likely responsible for the acceleration of the bulk of Galactic cosmic rays (CRs). To firmly establish the SNR paradigm for the origin of cosmic rays, it should be confirmed that protons are indeed accelerated in, and released from, SNRs with the appropriate flux and spectrum. This can be done by detailed theoretical models which account for microphysics of acceleration and various radiation processes of hadrons and leptons. The current generation of Cherenkov telescopes has insufficient sensitivity to constrain theoretical models. A new facility, the Cherenkov Telescope Array (CTA), will have superior capabilities and may finally resolve this long standing issue of high-energy astrophysics. We want to assess the capabilities of CTA to reveal the physics of various types of SNRs in the initial 2000 years of their evolution. During this time, the efficiency to accelerate cosmic rays is highest. We perform time-dependent simulations of the hydrodynamics, the magnetic fields, the cosmic-ray acceleration, and the non-thermal emission for type Ia, Ic and IIP SNRs. We calculate the CTA response to the γ-ray emission from these SNRs for various ages and distances, and we perform a realistic analysis of the simulated data. We derive distance limits for the detectability and resolvability of these SNR types at several ages. We test the ability of CTA to reconstruct their morphological and spectral parameters as a function of their distance. Finally, we estimate how well CTA data will constrain the theoretical models. 相似文献
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Long TeV γ-ray campaigns have been carried out to study the spectrum, variability and duty cycle of the BL Lac object Markarian 421. These campaigns have given some evidence of the presence of protons in the jet: (i) Its spectral energy distribution which shows two main peaks; one at low energies (∼1 keV) and the other at high energies (hundreds of GeV), has been described by using synchrotron proton blazar model. (ii) The study of the variability at GeV γ-rays and X-rays has indicated no significant correlation. (iii) TeV γ-ray detections without activity in X-rays, called “orphan flares” have been observed in this object.Recently, The Telescope Array Collaboration reported the arrival of 72 ultra-high-energy cosmic rays with some of them possibly related to the direction of Markarian 421. The IceCube Collaboration reported the detection of 37 extraterrestrial neutrinos in the TeV–PeV energy range collected during three consecutive years. In particular, no neutrino track events were associated with this source. In this paper, we consider the proton–photon interactions to correlate the TeV γ-ray fluxes reported by long campaigns with the neutrino and ultra-high-energy cosmic ray observations around this blazar. Considering the results reported by The IceCube and Telescope Array Collaborations, we found that only from ∼25% to 70% of TeV fluxes described with a power law function with exponential cutoff can come from the proton–photon interactions. 相似文献
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A consistent approach to the frequency analysis of hydrologic data in arid and semiarid regions, i.e. the data series containing several zero values (e.g. monthly precipitation in dry seasons, annual peak flow discharges, etc.), requires using discontinuous probability distribution functions. Such an approach has received relatively limited attention. Along the lines of physically based models, the extensions of the Muskingum‐based models to three parameter forms are considered. Using 44 peak flow series from the USGS data bank, the fitting ability of four three‐parameter models was investigated: (1) the Dirac delta combined with Gamma distribution; (2) the Dirac delta combined with two‐parameter generalized Pareto distribution; (3) the Dirac delta combined with two‐parameter Weibull (DWe) distribution; (4) the kinematic diffusion with one additional parameter that controls the probability of the zero event (KD3). The goodness of fit of the models was assessed and compared both by evaluation of discrepancies between the results of both estimation methods (i.e. the method of moments (MOM) and the maximum likelihood method (MLM)) and using the log of likelihood function as a criterion. In most cases, the DWe distribution with MLM‐estimated parameters showed the best fit of all the three‐parameter models. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Direct observations or deduced analysis indicate clearly that formation of intense fluxes of relativistic electrons is an important ingredient in the evolution of numerous active magnetized plasma systems. Examples of relativistic electron energization include the recovery phase of a planetary magnetic storm, post solar flare coronal activity and the afterglow of gamma ray bursts. It is suggested that there exists a universal mechanism, which may explain electron energization at the vastly different magnetized plasma environments. The favorite configuration consists of an inhomogeneous magnetic field anchored at a given magnetic structure and excitation of whistler waves due to external injection of low-energy non-isotropic electrons. The energization proceeds as a bootstrap process due to interaction with the propagating whistler waves along the inhomogeneous magnetic field. 相似文献
9.
O. Reimer P. F. Michelson R. A. Cameron S. W. Digel D. J. Thompson K. S. Wood 《Astrophysics and Space Science》2007,309(1-4):523-526
Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large
Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory.
Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars;
(2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially
at high galactic latitudes; (4) simultaneous broad-band blazar monitoring; (5) characterization of gamma-ray transients, including
gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification
and characterization. Several of these activities are needed to be in place before launch.
相似文献
10.
同位素段、亚段乃至次亚段的划分实质上是定义不同级别 (层次 )的气候事件 ,为全球不同级别气候事件的对比提供参照。但已有的研究可能受区域性因素及记录本身条件所限 ,对同位素亚段、次亚段划分的数目及对比不尽一致。基于太阳辐射曲线、柴达木盆地高分辨率自然伽玛 (GR)曲线及其他相关气候记录的对比研究发现 ,同位素亚段的划分与太阳辐射曲线岁差周期间存在着明确的对应关系 ,据此对 0 .9Ma以来同位素亚段划分进行补充和校正。基于气候层次的观点 ,建议以太阳辐射曲线为参照 ,对同位素亚段重新进行系统命名 ,在轨道尺度变化这一级取消次亚段 ,即完全按照太阳辐射曲线峰值进行亚段编号。 相似文献