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1.
We present an analysis of a high-amplitude event in the flux curve of component A of the gravitational lens QSO 2237+0305 observed by the OGLE and GLITP groups in autumn 1999. Hypothesizing this event to be associated with microlensing of a fold caustic, we analyzed the observational data using a method for the successive reconstruction of branches of the one-dimensional strip brightness distribution across the source corresponding to positive and negative arguments. The search for the branches was carried out on compact sets of nonnegative, monotonically nonincreasing, convex downward functions. The resulting shape of the strip brightness distribution for the accretion disk of the quasar is in agreement with results obtained earlier via model fitting. Features in the lensing curve that could be associated with curvature of the caustic, nearness of a cusp, or the influence of nearby caustics are noted. 相似文献
2.
This paper describes a method for analyzing observations of the passage of a star through a gravitational lensing caustic that enables the derivation of information about the brightness distribution across the stellar disk without knowledge of the lens parameters. The ill-posed inverse problem of reconstructing a one-dimensional strip brightness distribution across the stellar disk is solved using a regularization method, taking into account the non-negative nature of this function. Assuming the source is circularly symmetric, the search for the radial brightness distribution is carried out over compact sets of upward-convex, non-negative functions or functions that do not grow with distance from the stellar center. The method is used to analyze the gravitational microlensing event MACHO 98-SMC-1, of a star in the Small Magellanic Cloud, obtained by the PLANET international group. The resulting brightness distribution is compared with computations of limb darkening for model stellar atmospheres. 相似文献
3.
M. B. Bogdanov 《Astronomy Reports》2001,45(12):929-934
In the process of their evolution, small-scale clusters of weakly interacting massive particles (WIMPs) that formed in the early Universe can acquire rotational momentum and spheroidal shape. Even small oblateness of a cluster similar to that of the critical Roche surface can lead to the appearance of caustics in the plane of a source lensed by the object. The multiple source images that form in this case cannot be resolved in modern observations, and the cluster behaves like a noncompact spheroidal lens. The caustic crossing that occurs in the case of relative motion of the observer, the cluster of particles, and the lensed star can produce a large variety of flux curves, including those such as have been observed during microlensing events and interpreted as manifestations of binary gravitational lenses. Therefore, we cannot rule out the possibility that at least some of these events might actually be associated with clusters of WIMPs. 相似文献
4.
M. B. Bogdanov 《Astronomy Reports》2014,58(10):688-691
The amplification coefficient for gravitational lensing of a point source in the linear-caustic approximation is compared with exact values calculated for a lens comprised of two point masses. Even in the most favorable case for the caustic crossing, the error in the amplification coefficient remains below 1% only for distances to the caustic not exceeding 0.01 of the Einstein radius. 相似文献
5.
We consider observable effects during the gravitational microlensing of stars of finite angular size with a given brightness distribution across their disks by exotic objects whose space-time environment is described with the NUT metric. We demonstrate that, under certain conditions, the microlensing light curves and chromatic effects due to the wavelength dependence of the disk brightness distributions can differ considerably from those observed for a Schwarzschild gravitational lens, so that their analysis can facilitate the identification of such objects. 相似文献
6.
A. F. Zakharov 《Astronomy Reports》2006,50(2):79-90
Gravitational lensing is a powerful tool for studies of the distribution of matter (including dark matter) in the Universe. The characteristic angular separation of images and characteristic variability time scale depend on the characteristic masses of the gravitational lenses. The construction of the RADIOASTRON space interferometer in the coming years will provide qualitatively new conditions for investigations of microlensing of distant quasars in the radio, since it will become possible not only to resolve individual microimages of these quasars, but also to observe astrometric microlensing (i.e., the shift of an image of a distant quasar, sometimes called weak microlensing). Astrometric microlensing by compact objects in the Galactic halo is not a very significant effect for the RADIOASTRON interferometer, since the probability of such events is low and the characteristic time scales involved appreciably exceed the proposed operational lifetime of the interferometer. 相似文献
7.
Using a model-independent technique, we have reconstructed a one-dimensional strip distribution of the brightness over a stellar disk from observations of microlensing of a Galactic bulge star by a caustic of the binary gravitational lens OGLE-1999-BUL-23, obtained by the international PLANET group. The ill-posed inverse problem was solved using a regularization method taking into account the non-negativity of the brightness distribution. The radial brightness distribution was searched for on a compact set of convex-upward, monotonically non-increasing, non-negative functions, assuming that the source is circularly symmetrical. The reconstructed brightness distribution is compared with the results of model fitting and limb-darkening calculations based on models of stellar atmospheres. 相似文献
8.
V. N. Shalyapin 《Astronomy Reports》2006,50(9):699-707
A procedure for calculating two-dimensional power spectra of microlensing magnification fields is presented. In the absence of a shift, the one-dimensional projections of the power spectra P(k) corresponding to the light curve of a point source moving in a linear trajectory can be approximated by the expression (a 2 + k 2)?1/2 (where a = const). The power spectrum of an extended source is treated like the product of the power spectrum of a point source and the power spectrum of the brightness distribution of the extended source. The effect of the extent of the source is that it acts like a filter, suppressing high-frequency components in the spectrum. Based on eight years of monitoring of the quad gravitational lens Q2237+0305 by the OGLE group, power spectra for all four images are constructed and the (temporal) size of the radiating region of the quasar in the V filter is estimated to be 24 ± 6 days; given the constraints on the transverse velocity of the lensing galaxy (<600 km/s), the linear size turns out to be <1015 cm. 相似文献
9.
A statistical study of motions of images of distant extragalactic sources, such as quasars on the celestial sphere, due to
the action of weak gravitational microlensing is presented. It was assumed that the parallax of the lens was 10 milliarcseconds
(mas), the mass of the lens was 1 M
⊙, and the proper motion was μ = 30 mas. The initial point for the motion of the lens (a star in our Galaxy) was taken to be
the boundary of a region with a radius of ϑ = 100 mas and its center coincident with the distant source. The simulations for
each trajectory were carried out in steps, with the time step being 0.1 year. The number of sources “launched” over the computational
period was 5000. The appearance of the trajectories for the source images is presented; 57% of the total number of sources
that participated in the simulations showed motions of 0.7–1.0 mas.
Original Russian Text ? T.A. Kalinina, M.S. Pshirkov, 2006, published in Astronomicheskiĭ Zhurnal, 2006, Vol. 83, No. 6, pp.
483–488. 相似文献
10.
11.
A technique is proposed for the successive reconstruction of the branches of the strip brightness distribution for a quasar accretion disk via the analysis of observations of high magnification flux events in the multiple quasar images produced by a gravitational lens. The distribution branches are searched for on compact sets of nonnegative, monotonically nonincreasing, convex downward functions. The results of numerical simulations and application of the technique to real observations show that the solution obtained is stable against random noise. Analysis of the light curve of a high magnification event in image C of the gravitational lens QSO 2237+0305 observed by the OGLE group in summer 1999 has yielded the form of the strip brightness distribution in the accretion disk of the lensed quasar. The results are consistent with the hypothesis that the quasar disk was scanned by a fold caustic. The form of the strip distribution is consistent with the expected appearance of an accretion disk rotating around a supermassive black hole. 相似文献
12.
The paper presents a catalog of supermassive black holes (SMBHs) sharpened for interferometric observations at millimeter and submillimeter wavelengths, based on open sources. The catalog includes the object’s name, coordinates, angular size, and mass, the angular size of the gravitational radius of the SMBH, and the integrated radio flux associated with the radiosource concluding the SMBH at 20?900 GHz, planned for the Event Horizon Telescope, the future space mission Millimetron, and others. The catalog is intended for use during planning of interferometric observations of SMBH shadows.
相似文献13.
E. P. Velikhov K. R. Sychugov V. M. Chechetkin A. Yu. Lugovskii A. V. Koldoba 《Astronomy Reports》2012,56(2):84-95
We investigate the role of the magnetic field in the collapse of a gas-dust cloud into a massive gravitating object. Observations
of one such object (G31.41) indicate that the magnetic field has an hourglass shape oriented along the rotation axis of the
matter, due to the freezing-in of the magnetic-field lines in the accreting matter. It is believed that accretion in stellar
disks is associated with the transport of angular momentum from the center to the periphery, which could be initiated by large-scale
vortex structures arising in the presence of unstable rotational flows of matter. The numerical simulations have established
that the equilibrium configuration of a gas-dust disk rotating in a spherically symmetrical gravitational potential is subject
to the development of strong instability in the presence of a weak magnetic field. It is shown that the development of instability
leads to a transport of angular momentum to the disk periphery by large-scale vortex structures, together with the accretion
of matter onto the gravitating object. The magnetic-field lines near the equator take on a chaotic character, but an hourglass
configuration is observed near the rotation axis, in agreement with observations. 相似文献
14.
本文从研究公转角动量各自独立的星云状物质演化成原始天体开始，着重讨论由天体内部力源分布不均衡而产生的物质对流运动理论，地球周围引力场特征及响应，绕银心公转运行的地球壳、核相对运动特征．大陆地壳大规模经向水平运动周期与银河年的关系，以及它们与中前地质构造运动旋回潮的对此。从而证实：天体内部物质相对运动一地壳大规模经面水平运动行为，是天体遵守公转角动量守恒的一种反映。 相似文献
15.
重力场定义的澄清 总被引：3，自引：1，他引：2
《朗曼现代英文词典》(LongmanModernEnglishDictionary)、《牛津高阶英汉双解词典》(OxfordAdvancedLearner’sEnglish ChineseDictionary)、《韦氏词典》(Merriam Webster’sNewCollegiateDictionary)、作为地球物理专业词汇定义源的《勘探地球物理百科词典》(EncyclopedicDictionaryofExplorationGeo physics)以及中国的一些重力教科书、专著及词典 ,把重力场定义为重力或重力作用存在的空间 ,重力效应可以测量的空间 ,即 :力或重力存在的空间。这个定义不同于国外英文地球物理教科书、专著及中、英、俄文场论教科书对重力场的定义 :空间中的重力。定义重力场为重力存在的空间 ,混淆了“场”本身及“场域”的概念 ,并不是一个标准的物理或地球物理定义 ,是一种误导。物理场是空间中存在的一种物理作用或效应 ,分布于引起它的场源体周围。两个物体之间存在着的相互作用力 ,通过每个物体引起的引力场给予另一个物体。重力场可以定义如下 :地球内部及其附近空间一点处存在的重力作用 ,或单位质量受到的重力。重力场是一种力或力场 ,存在于地球表面及其附近的空间。重力场不是空间 ,重力场的测量应当是在重力场存在的空间或场域中 ,而不是在重力场中进行。 相似文献
16.
The behavior of the gravitational potential outside the region where the main spiral arms of galaxies are located is investigated. The characteristic features of this behavior include nearly circular extensions of the main arms, which typically have an angular extent of 90°. It is natural to interpret these quarter-turn spirals as the response of the galactic disk to the gravitational potential of the main spiral arms. The theoretical models are supported by observational data for the brightness distributions in both normal (NGC 3631) and barred (NGC 1365) galaxies. 相似文献
17.
We discuss possible interpretations of the extragalactic double galaxy CSL-1. CSL-1 can be explained either as the projection of two morphologically identical galaxies or as the effect of gravitational lensing by a cosmic string. We discuss the first of these possibilities in detail. More accurate observations will enable unambiguous conclusions about the nature of CSL-1. 相似文献
18.
本文从研究公转角动量各自独立的星云状物质演化原始天体开始,着重讨论由天体内部力源分布不均衡而产生的物质对流运动理论,地球周围引力场特征及响应,绕银心公转运行的地球壳,核相对运动特征,大陆地壳大规模经向水平运动周期与银河年的关系,以及它们与中前地质构造运动旋回期的对比,从而产：天体内部物质相对运动－地壳大规模经面水平运动行为,是天体尊守以转角动量守恒的一种反映。 相似文献
19.
A. A. Shatskii 《Astronomy Reports》2004,48(7):525-533
It is shown that Einstein-Rosen bridges (wormholes)—hypothetical objects that topologically connect separate locations in the Universe—can be static solutions of the Einstein equations. The corresponding equations for bridges are reduced to a form convenient for their analysis and numerical solution. The matter forming the bridge must have a sufficiently hard and anisotropic equation of state. Our results are compared with a previously known analytic solution for a bridge, which is a special case of the general solution in the framework of general relativity. The deflection of photons by the bridge (gravitational lensing) is studied. 相似文献
20.
The Arp-Burbidge paradox (the enhanced density of distant quasars in the vicinity of some nearby galaxies) can potentially be explained as an effect of gravitational lensing within the existing cosmological paradigm. Distant, rich X-ray clusters, or even superclusters, of galaxies are observed along the lines of sight toward many of the objects on which this “paradox” is based. Such clusters can act as complex, transparent gravitational lenses, which can change the observed surface density of background objects due to the gravitational fields of both the cluster as a whole and of massive member galaxies, as well as of possible intergalactic globular clusters that may contain an appreciable fraction (～10%) of the dark matter in galaxy clusters. We have verified the statistical basis for the supposedly “paradoxical” observational facts using data from the SDSS catalog, and used the minimal spanning tree method to search for inhomogeneities in the surface distributions of 32 800 quasars in one region of the celestial sphere (α = 120°–260°, δ = 20°–70°). 相似文献