SIGMA observations of hard X-ray and soft gamma-ray emission from X-ray binaries

After more than two years of operation, the imaging γ-ray SIGMA telescope has accumulated several days of observation toward well known X-ray binaries. Four bright sources falling in this category have been detected so far: The pulsar GX 1+4 near the center of our galaxy, the stellar wind accreting system 4U 1700-377, and the black hole candidates Cygnus X-1 and GX 339-4. Moreover, SIGMA have observed three transients sources, which turned out to be also hard X-ray sources : The burster KS 1731-260, Tra X-1, and the Musca Nova. The properties of these systems in the SIGMA domain will be reviewed and a spectral distinction between black holes and neutron stars will be sketched.     

飞行器雷达罩设计方法的研究

详细分析了飞行器雷达罩设计过程中的基本问题。基于多目标优化设计方法建立了雷达罩结构参数求解的数学模型,给出了求解方法。考虑到雷达罩的安全使用要求,分析了雷达罩防雷击部件的基本要求,提出了设计方法,给出了防雷击部件布置的经验公式。同时还研究了用于飞行器雷达罩金属部件的吸波材料电磁波吸收机理,以及吸波材料电性能设计原理和基本布置准则     

Removing orbital debris with lasers

Orbital debris in low Earth orbit (LEO) are now sufficiently dense that the use of LEO space is threatened by runaway collision cascading. A problem predicted more than thirty years ago, the threat from debris larger than about 1 cm demands serious attention. A promising proposed solution uses a high power pulsed laser system on the Earth to make plasma jets on the objects, slowing them slightly, and causing them to re-enter and burn up in the atmosphere. In this paper, we reassess this approach in light of recent advances in low-cost, light-weight modular design for large mirrors, calculations of laser-induced orbit changes and in design of repetitive, multi-kilojoules lasers, that build on inertial fusion research. These advances now suggest that laser orbital debris removal (LODR) is the most cost-effective way to mitigate the debris problem. No other solutions have been proposed that address the whole problem of large and small debris. A LODR system will have multiple uses beyond debris removal. International cooperation will be essential for building and operating such a system.     

The Goddard Experiment Package?An Automated Space Telescope

The Goddard Experiment Package will measure the ultraviolet spectral emittance of stars and nebulae. It has a spectral resolution of 2 ? in the 1050-? to 4000-? band. The telescope has a 38-inch clear aperture and automatically reduces the spectral data to digital form. Guidance accuracy is 1 of second arc.     

Analysis of Performance Degradation in CdS Solar Cells

The effect of changes in five physically meaningful parameters on the I-V (current-voltage) curve of a CdS solar cell is calculated. Comparisons between the calculated data and performance data obtained from degraded solar cells are made. The parameter that changed to cause the degradation in each cell becomes apparent.     

捷联式天线平台的稳定性研究

将Rudin提出的红外成像捷联稳定模型用于天线平台的稳定,并应用不变性原理,采取匹配滤波方法,提高了稳定平台的解耦精度.具体仿真结果表明:在0.5 Hz~1.0 Hz频段解耦精度提高了35 dB.同时,在考虑传感器测量噪声的情况下,对天线平台的稳定误差进行了仿真分析,结果显示,传感器测量噪声对稳定误差有较大的影响,但通过滤波稳定误差可减小50%左右.      

Analytical approach to cosmic ray ionization by nuclei with charge Z in the middle atmosphere – Distribution of galactic CR effects

The effects of galactic and solar cosmic rays (CR) in the middle atmosphere are considered in this work. A new analytical approach for CR ionization by protons and nuclei with charge Z in the lower ionosphere and middle atmosphere is developed in this paper. For this purpose the ionization losses (dE/dh) according to the Bohr–Bethe–Bloch formula for the energetic charged particles are approximated in three different energy intervals. More accurate expressions for energy decrease E(h) and electron production rate profiles q(h) are derived. The obtained formulas allow comparatively easy computer programming. The integrand in q(h) gives the possibility for application of adequate numerical methods – such as Romberg method or Gauss quadrature, for the solution of the mathematical problem. On this way the process of interaction of cosmic ray particles with the upper, middle and lower atmosphere will be described much more realistically. Computations for cosmic ray ionization in the middle atmosphere are made. The full CR composition is taken into account: protons, Helium (α-particles), light L, medium M, heavy H and very heavy VH group of nuclei.     

The Crab pulsar seen with AquEYE at Asiago Cima Ekar observatory

We are developing fast photon-counter instruments to study the rapid variability of astrophysical sources by time tagging photon arrival times with unprecedented accuracy, making use of a Rubidium clock and GPS receiver. The first realization of such optical photon-counters, dubbed AquEYE (the Asiago Quantum Eye), was mounted in 2008 at the 182 cm Copernicus Observatory in Asiago. AquEYE observed the Crab pulsar several times and collected data of extraordinary quality that allowed us to perform accurate optical timing of the Crab pulsar and to study the pulse shape stability on a timescale from days to years with an excellent definition. Our results reinforce the evidence for decadal stability of the inclination angle between the spin and magnetic axis of the Crab pulsar. Future realizations of our instrument will make use of the Galileo Global Navigation Satellite System (GNSS) time signal.     

An investigation of small GOES flares with intense hard X-ray bursts

Most solar flare observations show that intense hard X-ray bursts come from large flares that have a large GOES classification (large peak 1 – 8 Å flux). This correlation, known as the “Big Flare Syndrome”, suggests that more intense flares tend to have harder spectra. We have observed 7 flares that are exceptions to this. These flares have small GOES classifications ranging from B1.4 to C5.5 and peak hard X-ray count rates similar to those often observed from M class flares. This paper examines the cause of this anomoly using the Yohkoh Soft X-Ray Telescope, Hard X-Ray Telescope, and Bragg Crystal Spectrometer. Two hypotheses are proposed for the exceptions: (1) flares with multiple magnetic loops and common footpoints, producing multiple hard X-ray emission regions and low density thermal plasma distributed over a large volume, and (2) high densities in the magnetic loops restricting the propagation of the non-thermal electrons in the loop after magnetic reconnection has occurred and suppressing chromospheric evaporation. Two of the flares support the first hypothesis. The other flares either have data missing or are too small to be properly analysed by the Yohkoh instruments.