Rapid short-term pulse-period variations in Vela X-1 (4U 0900-40)

Results are presented of an analysis of 83 days of 2–12 keV X-ray observations of Vela X-1 (4U 0900-40) obtained during three separate pointings with the ESA COS-B satellite. The pulsation period is shown to undergo very rapid intrinsic changes, at a rate of up to during intervals of a few days. The lower values of which were previously observed over longer intervals, appear to result from an averaging-out of these rapid changes. It is argued, that the transfer of angular momentum to the neutron star by the accreting matter is very unlikely to be sufficient to explain these pulsation-period changes. An alternative explanation is suggested.     

An identification for GEMINGA: A review of all the available data

Dedicated X-ray, optical and radio observations aimed at the identification of the bright γ-ray source 2CG195+04 (GEMINGA) are presented. A very promising candidate is found and its properties are discussed in the context of possible astrophysical scenarios.     

The MESSENGER Gamma-Ray and Neutron Spectrometer

A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery Program mission to the planet Mercury. Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched successfully in 2004 and will journey more than six years before entering Mercury orbit to begin a one-year investigation. The GRNS instrument forms part of the geochemistry investigation and will yield maps of the elemental composition of the planet surface. Major elements include H, O, Na, Mg, Si, Ca, Ti, Fe, K, and Th. The Gamma-Ray Spectrometer (GRS) portion detects gamma-ray emissions in the 0.1- to 10-MeV energy range and achieves an energy resolution of 3.5 keV full-width at half-maximum for ⁶⁰Co (1332 keV). It is the first interplanetary use of a mechanically cooled Ge detector. Special construction techniques provide the necessary thermal isolation to maintain the sensor’s encapsulated detector at cryogenic temperatures (90 K) despite the intense thermal environment. Given the mission constraints, the GRS sensor is necessarily body-mounted to the spacecraft, but the outer housing is equipped with an anticoincidence shield to reduce the background from charged particles. The Neutron Spectrometer (NS) sensor consists of a sandwich of three scintillation detectors working in concert to measure the flux of ejected neutrons in three energy ranges from thermal to ∼7 MeV. The NS is particularly sensitive to H content and will help resolve the composition of Mercury’s polar deposits. This paper provides an overview of the Gamma-Ray and Neutron Spectrometer and describes its science and measurement objectives, the design and operation of the instrument, the ground calibration effort, and a look at some early in-flight data.     

低能自由空气电离室优化设计

借助于空气比释动能的基本定义和概念以及空气比释动能绝对测量的理论方法,分析了自由空气电离室可以作为空气比释动能绝对测量方法的原理和条件。通过平板型与圆柱型自由空气电离室的优劣比较,选择平板型作为研究对象,详细介绍了经典的平板型自由空气电离室,并通过理论分析计算以及模拟计算的方法,优化设计包括:光阑半径、空气衰减长度、极间距等低能自由空气电离室的关键几何尺寸,以最小化空气比释动能测量时产生的总不确定度。     

X射线脉冲星绝对定位法研究

研究和分析了脉冲星定位方法中的绝对定位法。通过一系列的公式和图表详细分析了定位算法的理论依据,同时还对整周模糊度问题的解算进行了研究。最后,利用MATLAB建立了一个简单模型,对定位算法进行仿真。结果表明定位准确度与星载原子钟准确度、脉冲星相位模型准确度以及相位观测误差有直接联系。     

The Burst Alert Telescope (BAT) on the SWIFT Midex Mission

he burst alert telescope (BAT) is one of three instruments on the Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and localizes the burst direction to an accuracy of 1–4 arcmin within 20 s after the start of the event. The GRB trigger initiates an autonomous spacecraft slew to point the two narrow field-of-view (FOV) instruments at the burst location within 20–70 s so to make follow-up X-ray and optical observations. The BAT is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed of 32,768 pieces of CdZnTe (4×4×2 mm), and the coded-aperture mask is composed of ∼52,000 pieces of lead (5×5×1 mm) with a 1-m separation between mask and detector plane. The BAT operates over the 15–150 keV energy range with ∼7 keV resolution, a sensitivity of ∼10⁻⁸ erg s⁻¹ cm⁻², and a 1.4 sr (half-coded) FOV. We expect to detect > 100 GRBs/year for a 2-year mission. The BAT also performs an all-sky hard X-ray survey with a sensitivity of ∼2 m Crab (systematic limit) and it serves as a hard X-ray transient monitor.     

Relative ionizations in the nearest interstellar gas

We compare CLOUDY predictions for the equilibrium ionization in the interstellar cloud surrounding the solar system with pick-up ion data. The incident radiation field includes contributions from hot stars, the emission from the conductive cloud boundary and the diffuse FUV back-ground. To within the observational uncertainties, CLOUDY predictions for the ratios n(He)/n(O), n(N)/n(O), n(Ne)/n(O), and n(He)/n(Ne) are consistent with pick-up ion data, provided that O and N are filtered by 50% in the heliopause region and the outer heliosphere as predicted by others. Thus, the steady-state ionization model and assumed radiation field appear approximately valid. However, the youth and low intervening column density towards the Vela pulsar leave open the possibility that the parent supernova explosion 10,500 years ago, and 200 pc distant, may also have affected LISM ionization, although the mechanism is uncertain. Support for this last possibility is provided by the apparent signature of the Vela explosion in the terrestrial geological record.Abbreviations ISM Interstellar Medium - FUV Far Ultraviolet - EUV Extreme Ultraviolet - SNR SN remnant - SXRB SXR Background - LISM Local Interstellar Matter     

稀土钇提高离子镀TiN膜层与基体结合力的研究

研究了稀土钇不同含量时对离子镀ＴｉＮ膜层与基体结合力的影响．用扫描电镜，俄歇谱仪，Ｘ射线衍射等手段，对加入稀土钇的ＴｉＮ膜层作了分析。结果表明，加适量稀土钇后，ＴｉＮ膜层与基体的结合力大大提高。其微观机制是，加稀土钇后，膜层相组成发生变化，在膜－基之间形成一过渡层，塑性相（Ｔｉ相）增加，脆性相（Ｔｉ２Ｎ）减少，从而减小了膜－基界面间的应力。此外，结果还表明，稀土钇能明显提高镀膜过程中钛料蒸发率，使成膜速率增加，在相同镀膜时间内ＴｉＮ膜层加厚。     

SiCP/Al复合材料脉冲氩弧焊接研究

研究在脉冲氩弧焊条件下铝基复合材料SiCp／2124Al的可焊性。通过正确选择填充材料和在焊接过程中加入微量脉冲，大大减弱了增强体SiC颗粒与基体Al之间的界面反应。拉伸实验和显微硬度测试表明，接头质量良好，与母材强度相比，接头的抗拉强度未见有大幅度下降；金相组织观察显示，焊缝组织致密、无夹杂和裂纹等缺陷。对接头进行X射线衍射相结构分析和拉伸断口扫描电镜观察等微观分析，并从热力学角度探讨焊接过程中抑制SiC／Al界面反应发生的机理，提出了在氩弧焊条件下获得高质量SiCp／Al焊接接头应采取的措施。     

Nitric oxide density enhancements due to solar flares

A differential emission measure technique is used to determine flare spectra using solar observations from the soft X-ray instruments aboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics and Solar Radiation and Climate Experiment satellites. We examine the effect of the solar flare soft X-ray energy input on the nitric oxide (NO) density in the lower thermosphere. The retrieved spectrum of the 28 October 2003 X18 flare is input to a photochemical thermospheric NO model to calculate the predicted flare NO enhancements. Model results are compared to Student Nitric Oxide Explorer Ultraviolet Spectrometer observations of this flare. We present results of this comparison and show that the model and data are in agreement. In addition, the NO density enhancements due to several flares are studied. We present results that show large solar flares can deposit the same amount of 0.1–2 and 0.1–7 nm energy to the thermosphere during a relatively short time as the Sun normally deposits in one day. The NO column density nearly doubles when the daily integrated energy above 5 J m⁻² is doubled.