The Density and Masses of Obscured Black Holes

Recent Chandra and XMM-Newton surveys have uncovered a large fraction of the obscured AGN responsible of the hard X-ray background. One of the most intriguing results of extensive programs of follow-up observations concerns the optical and near-infrared properties of the hard X-ray sources counterparts. More specifically, for a significant fraction of hard X-ray obscured sources the AGN responsible of the high X-ray luminosity remains elusive over a wide range of wavelengths from soft X-rays to near-infrared. This very observational result opens the possibility to investigate the host of bright obscured quasars in some detail. Here we briefly report on some preliminar results obtained for a small sample of elusive AGN in the HELLAS2XMM survey.     

Optical and X-ray observations of thermonuclear bursts from GS 1826-24 during September–October 2003

The results of optical (the RTT-150 telescope) and X-ray (the RXTE observatory) observations of the burster GS 1826-24 are presented. Emphasis was placed on analyzing the emissions during thermonuclear bursts. The results obtained allowed the size of the accretion disk in GS 1826-24 and the inclination of this binary to be estimated.     

The role of non-thermal electrons in the hydrogen and calcium lines of stellar flares

There is observational evidence showing that stellar and solar flares occur with a similar circumstance, although the former are usually much more energetic. It is expected that the bombardment by high-energy electrons is one of the chief heating processes of the flaring atmosphere. In this paper we study how a precipitating electron beam can influence the line profiles of Ly α , H α , Ca  ii K and λ 8542. We use a model atmosphere of a dMe star and make non-LTE computations taking into account the non-thermal collisional rates owing to the electron beam. The results show that the four lines can be enhanced to different extents. The relative enhancement increases with increasing formation height of the lines. Varying the energy flux of the electron beam has different effects on the four lines. The wings of Ly α and H α become increasingly broad with the beam flux; change of the Ca  ii K and λ 8542 lines, however, is most significant in the line centre. Varying the electron energy (i.e. the low-energy cut-off for a power-law beam) has a great influence on the Ly α line, but little on the H α and Ca  ii lines. An electron beam of higher energy precipitates deeper, thus producing less enhancement of the Ly α line. The Ly α /H α flux ratio is thus sensitive to the electron energy.     

磁场重联和日冕物质抛射

Basic processes of magnetic reconnection and observations of coronal mass ejection are introduced. A possible mechanism of CME caused by magnetic rcconnection in the current sheet of solar corona is suggested.     

AR5395及AR6659的贮能释能周期性

本文分析了了AR5395和AR6659的X射线耀斑活动周期性，耀斑强度周期的存在表明活动区的能量积累和释放过程具有可重复性，包括贮存的能量大小也具可重复性，计算得出AR5395的耀风强度周期为24．49小时，而AR6659的周期为57．39小时，耀斑指数按周期的分布证明在一个贮能周期中活动区贮存的能量大致相同，周期内的平均耀斑指数代表能量积累效率，AR6659较之AR5395有较长的能量积累周期和较高的能量积累效率．此外，本文还讨论了耀斑事件出现的周期．这种周期的长短代表活动区磁结构对于耀斑出现的稳定程度，并且，当活动区处于较高能量状态（即相对势场状态的偏离较大）时，出现耀斑不稳定性的可能性增加。     

Effects of Interference and Oxidation on the UV/Visible Rejection Properties of Filters for Soft X-ray Detectors

We report on UV/Visible transmission measurements of aluminum coated Lexan filters designed as UV blocking filters for soft x-ray detectors. Transmission of the filters in the 2300-8000 Å wavelength range is significantly higher than expected. It cannot be accounted for applying a simple slab model of the transmission and adopting material properties reported in the literature. We show that this is due to interference effects which are strongly dependent on the filter geometry, and to oxidation of exposed aluminum surfaces and/or chemical interaction with the plastic support. The results of this work have led to the redesign of the Advanced X-ray Astrophysics Facility High Resolution Camera UV blocking filters.     

On the Nature of the Variable Gamma-Ray Sources at Low Galactic Latitudes

Population studies of EGRET gamma-ray sources indicate that there is a distinctive population of bright sources at low galactic latitudes. The sources have a distribution consistent with that of young galactic objects, with a concentration toward the inner spiral arms. There is a subgroup that displays strong variability with timescales from days to months. Following an earlier suggestion by Kaufman Bernadó et al. (2002), we explore the possibility that these sources could be high-mass microquasars. Detailed models for the gamma-ray emission that include inverse Compton interactions of electrons in the relativistic jets and photons from all local fields (stellar UV photons, synchrotron photons, soft X-ray photons from the accretion disk, and hard X-ray photons from a corona) are presented. We conclude that microquasars are excellent candidates for the parent population of the subgroup of variable low-latitude EGRET sources.     

Outburst of the X-ray transient SAX J1818.6-1703 detected by the INTEGRAL observatory in September 2003

During the observation of the Galactic-center field by the INTEGRAL observatory on September 9, 2003, the IBIS/ISGRI gamma-ray telescope detected a short (several-hours-long) intense (～380 mCrab at the peak) outburst of hard radiation from the X-ray transient SAX J1818.6-1703. Previously, this source was observed only once in 1998 during a similar short outburst. We present the results of our localization, spectral and timing analyses of the object and briefly discuss the possible causes of the outburst. The release time of the bulk of the energy in such an outburst is appreciably shorter than the accretion (viscous) time that characterizes the flow of matter through a standard accretion disk.     

试谈利用科技手段鉴别古玉器

鉴别古玉的真伪,传统的方法主要是通过玉器的加工工艺、艺术风格(器型、文饰等)等时代特征来加以确认.然而,现代科技发展使古玉仿制已达到以假乱真的地步,仅凭经验难以做出有说服力的判断,需要借助科学仪器的帮助.本文通过对一兽面环的鉴定为例,用传统的宝石学测试,再经现代科学仪器、X射线衍射分析,经JCPDF检索,两者结合,最终得出了准确的结论.     

兰州第四纪黄土/古土壤序列物源演变: 来自于碳酸盐矿物的证据*

黄土/古土壤的物源研究对于揭示第四纪气候变化和青藏高原隆升历史具有重要意义。本研究以位于黄土高原西部1.4 Ma以来的兰州黄土/古土壤沉积序列为研究对象,基于X射线衍射技术分析了黄土/古土壤中的主要矿物组成,侧重于碳酸盐矿物含量,追溯了兰州黄土/古土壤的直接物源。结果显示: (1)1.4 Ma以来兰州地区黄土/古土壤沉积物的主要直接源区为柴达木盆地沙漠区和阿拉善干旱区。(2)基于二元混合模型计算的潜在原始源区对兰州黄土白云石和总碳酸盐矿物的相对贡献率以及长石与石英比值结果一致支持1.4 Ma以来兰州黄土原始物源发生了多次变化。1.4~1.1 Ma和0.9~0.3 Ma青藏高原东北缘造山带(昆仑山、祁连山)和中亚造山带对兰州黄土的贡献相当,而1.1~0.9 Ma和0.3 Ma以来,中亚造山带对兰州黄土的物源贡献增加,这可能分别是对中更新世气候转型和0.3 Ma以来青藏高原及邻近地区干冷气候增强的响应。1.15 Ma和0.8 Ma兰州黄土/古土壤中高的白云石含量、碳酸盐矿物总含量以及0.8 Ma长石与石英比值的快速升高可能是对“昆黄运动”的响应,进而造成了昆仑山、祁连山对黄土高原物源贡献的增加。