Glitch effects in ISOCAM Long Wave detector

One of the main limitations to the sensitivity of observations carried out withthe ISOCAM infrared camera comes from the responsivity variations and glitchescaused by impacts of charged particles. After more than 28 months of successfuloperations, the predicted glitch rate has been re-evaluated and compared toin-flight measurements. Glitch properties have been studied in orderto improve the removal algorithms, and thus the ultimate sensitivity of ISOCAM.All informations about the glitch phenomenon are very useful in order toprepare next space experiments.     

Monte-Carlo Simulations of Cosmic-ray and Internal Radiation Effects on ISOCAM on Board ISO

One of the main limitations to the sensitivity of the infrared camera ISOCAM on-board the Infrared Space Observatory (ISO) comes from responsivity variations and glitches caused by the impacts of charged particles in photo-detectors. Glitch rate measurements, glitch properties and removal methods have already been addressed during the first ISO detector workshop(Madrid, 1998) and published in a special issue of Experimental Astronomy. It appeared that glitch rate and most of glitch properties could be reproduced by Monte-Carlo simulations. This is very interesting in order to predict before launch the effect of charged particles in photo-detectors operated in space. This paper presents results of Monte-Carlo simulations of radiation effects on ISOCAM detectors. Glitch rates, spatial and energetic properties of glitches have been computed and are compared with measured values. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simulations of Galactic Cosmic Ray impacts onto the Herschel/PACS photoconductor arrays with Geant4 code

We present results of simulations performed with the Geant4 software code of the effects of Galactic Cosmic Ray impacts on the photoconductor arrays of the PACS instrument. This instrument is part of the ESA-Herschel payload, which will be launched in 2008 and will operate at the Lagrangian L2 point of the Sun-Earth system. Both the Satellite plus the cryostat (the shield) and the detector act as source of secondary events, affecting the detector performance. Secondary event rates originated within the detector and from the shield are of comparable intensity. The impacts deposit energy on each photoconductor pixel but do not affect the behaviour of nearby pixels. These latter are hit with a probability always lower than 7%. The energy deposited produces a spike which can be hundreds times larger than the noise. We then compare our simulations with proton irradiation tests carried out for one of the detector modules and follow the detector behaviour under ‘real’ conditions.     

Cosmic rays and the primordial gas

One of the most-outstanding problems in the gravitational collapse scenario of early structure formation is the cooling of primordial gas to allow for small-mass objects to form. As the neutral primordial gas is a poor radiator at temperatures   T ≤ 10⁴ K  , molecular hydrogen is needed for further cooling down to temperatures   T ∼ 100 K  . The formation of molecular hydrogen is catalyzed by the presence of free electrons, which could be provided by the ionization due to an early population of cosmic rays (CRs). In order to investigate this possibility, we developed a code to study the effects of ionizing CRs on the thermal and chemical evolution of primordial gas. We found that CRs can provide enough free electrons needed for the formation of molecular hydrogen, and therefore can increase the cooling ability of such primordial gas under following conditions. A dissociating photon flux with   F < 10⁻¹⁸ erg cm⁻² Hz⁻¹ s⁻¹  , initial temperature of the gas  ∼10³ K  , total gas number densities   n ≥ 1 cm⁻³  , and cosmic-ray sources with     .     

Energy dependence of Ti/Fe ratio in the Galactic cosmic rays measured by the ATIC-2 experiment

Titanium is a rare, secondary nucleus among Galactic cosmic rays. Using the Silicon matrix in the ATIC experiment, Titanium has been separated. The energy dependence of the Ti to Fe flux ratio in the energy region from 5 GeV per nucleon to about 500 GeV per nucleon is presented. The article was translated by the authors.     

宇宙线的超新星遗迹起源

宇宙线的起源是高能天体物理的核心问题之一.一直以来,超新星爆发被认为是能谱膝区以下宇宙线的主要来源.多波段观测表明,超新星遗迹有能力加速带电粒子至亚PeV (10~(15)eV)能量.扩散激波加速被认为是最有效的天体高能粒子加速机制之一,而超新星遗迹的大尺度激波正好为这一机制提供平台.近年来,一系列较高精度的地面和空间实验极大地推动了对宇宙线以及超新星遗迹的研究.新的观测事实挑战着传统的扩散激波加速模型以及其在银河系宇宙线超新星遗迹起源学说上的应用,深化了人们对宇宙高能现象的认识.结合超新星遗迹辐射能谱的时间演化特性,构建的时间依赖的超新星遗迹粒子加速模型,不仅能够解释200 GV附近宇宙线的能谱反常,还自然地形成能谱膝区,甚至可以将超新星遗迹粒子加速对宇宙线能谱的贡献延伸至踝区.该模型预期超新星遗迹中粒子的输运行为表现为湍流扩散,这需要未来的观测以及与粒子输运相关的等离子体数值模拟工作来进一步验证.     

On the role of injection in kinetic approaches to non-linear particle acceleration at non-relativistic shock waves

The dynamical reaction of the particles accelerated at a shock front by the first-order Fermi process can be determined within kinetic models that account for both the hydrodynamics of the shocked fluid and the transport of the accelerated particles. These models predict the appearance of multiple solutions, all physically allowed. We discuss here the role of injection in selecting the real solution, in the framework of a simple phenomenological recipe, which is a variation of what is sometimes referred to as thermal leakage. In this context we show that multiple solutions basically disappear and when they are present they are limited to rather peculiar values of the parameters. We also provide a quantitative calculation of the efficiency of particle acceleration at cosmic ray modified shocks and we identify the fraction of energy which is advected downstream and that of particles escaping the system from upstream infinity at the maximum momentum. The consequences of efficient particle acceleration for shock heating are also discussed.     

Simulation Study on High Energy Cosmic Electron Detection by Shower Image

Many projects have recently been carried out and proposed for observing high energy electrons since it is realized that cosmic ray electrons are very important when studying the dark matter particles and the acceleration mechanism of cosmic rays. An imaging calorimeter, BETS （Balloon-borne Electron Telescope with Scintillator fiber）, has been developed for this purpose. Using pattern analysis of the shower development, the electrons can be selected from those primary cosmic ray proton events with flux heights one-tenth that of the electrons. The Monte-Carlo simulation is indispensable for the instrument design, the signal trigger and the data analysis. We present different shower simulation codes and compare the simulation results with the beam test and the flight data of BETS. We conclude that the code FLUKA2002 gives the most consistent results with the experimental data.     

Cosmic ray acceleration to very high energy through the non-linear amplification by cosmic rays of the seed magnetic field

The maximum energy for cosmic ray acceleration at supernova shock fronts is usually thought to be limited to around 10¹⁴–10¹⁵ eV by the size of the shock and the time for which it propagates at high velocity. We show that the magnetic field can be amplified non-linearly by the cosmic rays to many times the pre-shock value, thus increasing the acceleration rate and facilitating acceleration to energies well above 10¹⁵ eV. A supernova remnant expanding into a uniform circumstellar medium may accelerate protons to 10¹⁷ eV and heavy ions, with charge Ze , to Z ×10¹⁷ eV. Expansion into a pre-existing stellar wind may increase the maximum cosmic ray energy by a further factor of 10.     

Cosmic rays and other nonsense in astronomical CCD imagers

Cosmic-ray muons make recognizable straight tracks in the new-generation CCD's with thick sensitive regions. Wandering tracks (‘worms’), which we identify with multiply-scattered low-energy electrons, are readily recognized as different from the muon tracks. These appear to be mostly recoils from Compton-scattered gamma rays, although worms are also produced directly by beta emitters in dewar windows and field lenses. The gamma rays are mostly byproducts of ⁴⁰K decay and the U and Th decay chains. Trace amounts of these elements are nearly always present in concrete and other materials. The direct betas can be eliminated and the Compton recoils can be reduced significantly by the judicious choice of materials and shielding. The cosmic-ray muon rate is irreducible. Our conclusions are supported by tests at the Lawrence Berkeley National Laboratory low-level counting facilities in Berkeley and 180 m underground at Oroville, California. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于暗物质粒子探测卫星的宇宙线直接探测研究

高能宇宙线的起源、加速和传播是重大的前沿科学问题,回答该问题需要对宇宙线的能谱、各向异性以及各类高能天体电磁辐射进行精确观测.通过空间粒子探测器对宇宙线各成分能谱的直接测量是研究宇宙线物理问题的重要手段.中国于2015年底发射并持续运行至今的暗物质粒子探测卫星以其大接受度、高能量分辨率等特点,在宇宙线直接探测方面取得了系列重要成果,揭示出质子、氦核、硼碳和硼氧比例等宇宙线能谱的新结构,为理解宇宙线起源等科学问题提供了新的依据.介绍了暗物质粒子探测卫星的仪器设置、运行状况、科学成果及其物理意义.     

Statistical Investigation on Galactic Cosmic Rays and Solar Wind Variation Based on ACE Observations

Based on the Galactic Cosmic Rays (GCRs) and plasma observations from ACE spacecraft, the relation between GCR counts and solar wind parameters during the two periods of solar minimums (the years of 2007.0-2009.0 and 2016.5-2019.0) was analyzed by means of the Superposed Epoch Analysis (SEA) method. The results indicate that GCRs are strongly modulated by Co-rotating Interaction Regions (CIRs) in solar wind, the Stream Interfaces (SIs) sandwiched between fast and slow solar wind are closely related with the depression of GCR counts. The mechanism of the GCR variation was investigated through the empirical diffusion coefficients. The so-called “snow-plough” effect of GCR variation prior to the SI crossing appears during the first period, then the GCR counts decrease after the crossing, which corresponds to the sudden drop of diffusion coefficient at the SI. However, this effect is not observed for the second period, the decrease of GCR counts may be caused by the enhancement of the diffusion coefficient after the SI crossing. Moreover, Heliospheric Current Sheet (HCS) correlates with GCR counts well, the GCRs drift along the current sheet, and then accumulate to a pileup structure. The interplay between drift and diffusion determines the GCR distribution and variation at a heliocentric distance of 1 AU.     

An Investigation on Anisotropy of Cosmic Rays with a Small Air Shower Array

We have studied anisotropy of cosmic rays with an Extensive Air Shower(EAS) array in Tehran 1200 m above sea level. In analyzing the data set, we have used appropriate techniques of analysis and considered environmental effects. An asymmetry has been observed in the azimuthal distribution of EAS of cosmic rays because of magnetic field of the Earth.     

The Latitudinal Effect of Corotating Interaction Regions on Galactic Cosmic Rays

The response of galactic cosmic rays (GCRs) to an isolated enhancement of the non-axisymmetric component of the solar open magnetic field between June and November 1996 is investigated by using a combination of solar observations and numerical modelling of the interplanetary medium. The most obvious coronal hole visible from Earth at the time had little shielding effect on the flux of GCRs, as measured at Earth by neutron monitors. It is found that the evolution of the corotating interaction regions generated by a less obvious coronal hole was the principal controlling factor. Moreover, we demonstrate the imprint of the latitudinal and longitudinal evolution of that coronal hole on the variation of GCRs. The latitudinal extent of this solar minimum corotating interaction region had a determining, but local, shielding effect on GCRs, confirming previous modelling results.     

长γ暴时域功率密度谱与光度的强相关

提供一个基于光变曲线的长γ暴光度的估计量．对BASTE记录到的12个已知红移的γ暴，利用时域上的时变分析方法计算了各暴的功率密度谱，用功率密度的峰值P表征光变曲线变化的剧烈程度．通过拟合发现在共动坐标系P与γ暴的各向同性峰值光度L之间存在着相关关系．这是继Norris等和Reichart等发现时间延迟与光度、变化率与光度的相关性之后又一个γ暴时变特征量与其光度之间的相关关系．     

On gamma radiation from the magellanic clouds and galactic supernova remnants — Possible antiproton sources in the galaxy

Radiation from the Magellanic Clouds is discussed from the point of view of near future possibilities in observational γ-ray astronomy. The γ-ray fluxes expected according to the metagalactic and galactic theories of the origin of cosmic rays are compared. It is shown that the strongest test of the metagalactic hypothesis will be provided by a determination of the ratio of γ-ray fluxes from SMC and LMC. The γ-ray luminosity of a typical young supernova remnant that can generate sufficient antiprotons is estimated. It is shown that such remnants must have a short phase during which they are very powerful γ-ray emitters.