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601.
We present a method of a possible physical identification of the static and axially symmetric Weyl-type vacuum γ and nγ metrics.
This method, in which no interior solutions of any kind are involved, is based on the comparison of the far-field forms of
the γ and nγ metrics, and of the far-field form of the metric tensor due to a bounded gravitating perfect-fluid source given
correctly to post-Newtonian accuracy. The parameters of the vacuum solutions are expressed in terms of physical parameters
of a prolate fluid source, namely total mass-energy, semiaxes and eccentricity, defined consistently to post-Newtonian accuracy.
The results, based on the otherwise arbitrary fluid source, appear physically general. Possible astrophysical candidates for
the far-field γ andnγ metrics are proposed, based on the conditions imposed on them by the identification method. The advantages and deficiencies
of the identification method are briefly discussed. 相似文献
602.
603.
Rob Cavallo Keith A. Arnaud Virginia Trimble 《Journal of Astrophysics and Astronomy》1993,14(3-4):141-143
Pointed ROSAT PSPC exposures of 9277 and 6992 sec, directed toward the nearby, single, cool, magnetic white dwarfs GR 290
and EG 250 yielded no counts significantly above the expected background rate. The corresponding flux limits (for an assumed
source temperature of l keV) are 1.0 and 1.7 × 10−14erg cm−2 s−1, within the 0.1–2.5 keV bandpass of the instrument (99% confidence limits). This is more than an order of magnitude below
the tentative detection level (for GR 290) and limits (for four other similar stars) obtained from archival Einstein data
in 1991. The corresponding limits on coronal electron density are comparable with those implied if cyclotron emission is not
responsible for any of the features observed in the optical spectra of magnetic white dwarfs. X-ray data currently provide
no evidence for the existence of coronae around these stars. A final long observation (25,000 sec of GD 356) is scheduled
for later this year on ROSAT, along with coordinated EUVE observations. 相似文献
604.
河南金矿主要分布在小秦岭地区,其次是桐柏山、崤山─熊耳山地区。含矿地层为前寒武纪的片麻岩-混合岩、片岩-变粒岩和轻微变质的绿片岩,原岩皆属中基性火山岩夹火山沉积岩;控矿构造以近东西向和北东向为主,与成矿关系密切的岩浆岩主要是燕山期花岗岩及有关脉岩。本文拟从地层、构造、岩浆岩控矿特点入手,通过金矿的成矿机制试图揭示小秦岭─桐柏山地区金矿成矿模式。 相似文献
605.
本文报道南天区5GHzVLBI普查式观测结果.首次观测是在1992年11月期间进行的,共观测了23个河外射电源,获得了20个河外射电源的VLBI高分辨率的射电图象.有15个射电源呈现核喷流结构,1个有双向喷流,3个未分解,末发现有致密观源.在16个核喷流(包括一个双向喷流源)源中有11个呈现弯曲喷流现象.此外还首次发现有3个源中可能有超光速运动现象. 相似文献
606.
视超光速源的统计分析 总被引:2,自引:0,他引:2
本文收集了视超光速源样本的有关观测数据,在同步加速自康普顿散射机制下导出了各源的多普勒因子,再利用视超光速源的相对论射束模型计算样本源的有关物理量,如射电光度和亮温度,并与它们的观测值作直接的比较,得到较好的相关结果。这些结果支持了活动星系核中具有相对论射束运动的假设。同时我们比较了样本源的射电、光学、X射线的发现它们之间有一定的相关性,说明在不同波段上的辐射机制可能存在某种联系。 相似文献
607.
Karen M. Leighly 《Astrophysics and Space Science》2005,300(1-3):137-142
Significant (marginal) detections of periodic signals have been recently reported in 3 (4) Active Galactic Nuclei. Three of
the detections were obtained from long EUVE light curves of moderate-luminosity Seyfert galaxies; the fourth was discovered
in Chandra data from the low-luminosity Seyfert 1 galaxy NGC 4395. When compared with Cyg X-1, I find that the period is related
to the luminosity as P∝ L2/3 rather than the expected one-to-one relationship. This result might be explained if the QPO is associated with the inner
edge of the optically thick accretion disk, and the inner-edge radius depends on the source luminosity (or black hole mass).
A discussion of uncertainties in the period detection methodology is also discussed. 相似文献
608.
Gregory S. Rose 《The Professional geographer》1985,37(1):66-72
A variety of sources provides different levels of information about the origins of nineteenth century migrants to the Midwest. The advantages and disadvantages of four of the most common records, the federal census, land office records, genealogical collections, and county histories/biographies/atlases, are examined. Characteristics considered are the specific types of data provided, extent of coverage, level of detail, statistical reliability, and accessibility. Examples of studies using each record type are cited. 相似文献
609.
P. N. Bhat P. V. Ramana Murthy P. R. Vishwanath 《Journal of Astrophysics and Astronomy》1988,9(3):155-160
Cygnus X-3, an X-ray binary with an orbital period 4.8 hr was seen to be emitting γ-rays with the same period at TeV energies
by several groups. In addition the Durham group (Chadwicket al. 1985) published their observations on the existence of a pulsar in the Cyg X-3 system, emitting TeV γ-rays with a periodicity
of approximately 12.6 ms. We observed this object during 1986 October-November and did not detect any pulsed emission of TeV
γ-rays in the range of periods from 12.5850 to 12.5967 ms. 相似文献
610.
N. V. Abrosimov 《Experimental Astronomy》2005,20(1-3):185-194
Both Ge1−x
Si
x
mosaic crystals and Si1−x
Ge
x
crystals with gradient of composition could be grown using the modified Czochralski technique to produce the diffracting elements for the MAX gamma ray telescope. Although many elements cut from the mosaic crystal and used before for CLAIRE gamma ray telescope had an efficiency up to 20%, the overall efficiency of the lens was about 8.1 ± 0.7 %, which is more than twice lower than the theoretically predicted efficiency. Some causes of this behaviour are discussed. In addition to mosaic crystals, the growth of Si1−x
Ge
x
crystals with a gradient of composition and their properties are analysed. Such composition-gradient crystals could be a promising way to improve the diffraction efficiency of Laue lens for MAX. 相似文献