共查询到19条相似文献，搜索用时 203 毫秒
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在发现类星体的方法中,最有效的４ 种方法是：颜色方法,无缝光谱方法,射电方法和Ｘ射线方法。覆盖的波段为：射电波段,光学波段和Ｘ 射线波段。我们将４ 种方法联合在一起,应用于４ 个ＵＫＳｃｈｍｉｄｔ 天区。其目的是尽量减少选择效应,建立更完备的类星体巡天样本。本工作从１００２ 天区入手。已完成了Ｘ 射线选和部分光学选的分光观测工作。发现了一颗Ｂ＝ １５ ．０ 的亮类星体和一个Ｓｅｙｆｅｒｔ 对,其强Ｘ 射线辐射,是迄今首次观测到的。 相似文献
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本文概述了Einstein天文台IPC获得X射线流量和光度的统计结果,对混合样品,即光学选择类星体样品,射电选择类星体样品和X射线选择活动星系核样品,讨论了X射线光度与光学光度、射电光度、射电形态的关系以及它的演化性质。 相似文献
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活动星系核（AGN）是宇宙中最奇特的天体之一。它是真正意义上的全波天体，其中X射线波段的发射功率占到全波段功率的50％左右。AGN的X射线辐射研究涉及天体物理中的最基本问题，例如能量产生、辐射机制和宇宙论等，而Chandra X射线卫星的高分辨率图像和光谱对这一研究有着重要作用。以Chandra卫星的部分观测结果为例，简要介绍了几类不同类型AGN的X射线辐射研究进展：（1）宽吸收线类星体APM08279＋5255（z=3．91）的X射线谱分析，以及高红移类星体的观测概况；（2）Seyfert星系NGC 4151延展X射线发射问题的解决，及NGC 1068X射线辐射与光学波段的高激发态发射线（[OⅢ]λ5007）有很强相关性的发现；（3）6个BLLac天体样本的X射线环境分析；（4）射电星系X射线喷流的观测等。 相似文献
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《天文学进展》2015,(3)
活动星系核的能量反馈是星系形成理论模型中的一个重要物理过程,与星系所处的暗物质晕质量、星系中央大质量黑洞吸积率等因素有关。当前的半解析模型预测活动星系核反馈机制主要有两种模式:射电模式和类星体模式,前者主要发生在大质量暗晕中央的大质量星系中,后者主要由较小质量星系并合导致。利用斯隆数字化巡天(SDSS)提供的目前最大的类星体光谱观测样本,结合基于SDSS构建的星系群(团)表,从统计上分析了类星体的热光度和暗晕质量的分布情况。初步分析结果显示,在大质量暗晕中,类星体的热光度和所在暗晕的质量没有相关性,类星体所在暗晕的质量分布很广,进一步证实了高光度的类星体并不存在于大质量的暗晕中。 相似文献
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为了研究ROSATX射线选亮近类星体巡天的选择判据 ,从 1 995年 4月至 1 996年 1 0月期间 ,利用北京天文台 2 .1 6米望远镜进行了试验观测 ,发现了 73个类星体、2 7个赛弗特星系、1个BLLac候选体、1个白矮星和 1个激变变星 相似文献
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本文第1部份,描述从SAS-2卫星得到的能量大于100MeV的宇宙Υ射线数据来证认有Υ射线的活动星系核。11个类星体、3个BLLac天体和1个射电星系的Υ射线辐射已得到证认。 本文第2部分描述活动星系核对河外Υ射线背景辐射的影响。SAS-2的Υ辐射数据,已被用来测定类星体和赛弗特星系的Υ辐射绝对光度与光学绝对光度间的函数关系,并由此导出它们对河外Υ射线背景辐射的贡献。我们指出,类星体(B<20)、赛弗特星系(1型和1.5型)对35—100MeV能量范围的弥散Υ射线背景辐射有相当大的贡献(59％)。由此我们得出河外Υ射线背景辐射可能是由类星体和赛弗特星系这类活动星系产生的结论。 本文第3部份我们对3个有Υ辐射的活动星系核综合其Υ波段和其他波段的数据,以探索这些天体辐射的发射机制。这些综合的数据对发射机制给出严格的限制。我们指出,对这3个天体的数据,与同步自康普顿模型(SSC)的预计是一致的。 相似文献
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Yu Bai Yang Chen Xiang-Tao He Jiang-Hua Wu Qing-Kang Li Richard F.Green Wolfgang Voges 《中国天文和天体物理学报》2007,7(3):375-379
This is the third paper in a series connected with our Multiwavelength Quasar Survey. The survey is aimed to provide a quasar sample more complete than any previous survey by using a combined selection technique to reduce selection effects. We present the observational results for the X-ray candidates in field f836. We found 15 X-ray AGNs in this field of which eight are new discoveries. The X-ray data and optical spectra of these AGNs are given. We give the X-ray candidate selection criteria, which proved to be highly efficient in isolating X-ray AGNs. 相似文献
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This is the third paper in a series connected with our Multiwavelength Quasar Survey. The survey is aimed to provide a quasar sample more complete than any previous survey by using a combined selection technique to reduce selection effects. We present the observational results for the X-ray candidates in field f836. We found 15 X-ray AGNs in this field of which eight are new discoveries. The X-ray data and optical spectra of these AGNs are given. We give the X-ray candidate selection criteria, which proved to be highly efficient in isolating X-ray AGNs. 相似文献
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We aim to providea quasar sample that is more complete than any previous surveys by using a combined selection technique to reduce the selection effects. Here we present the observational results for the X-ray candidates in the field of the Leo Cluster. We found 33 X-ray AGNs in this field of which 10 are new discoveries. The X-ray data and optical spectra of these AGNs are given. We also study the near-IR properties of the X-ray-selected AGNs by using the data from 2MASS. Most of the AGNs in our sample span the color range 0.0 < B-J < 2.5, 1.0 < J-Ks < 2.0 and 0.5 < H-Ks < 1.2. 相似文献
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Radio sources of the RC catalog produced in 1980–1985 at RATAN-600 radio telescope based on a deep survey of a sky strip centered on the declination of the SS433 source are optically identified in the region overlapping with FIRST and SDSS surveys (about 132?° large). The NVSS catalog was used as the reference catalog for refining the coordinates of the radio sources. The morphology is found for about 75% of the objects of the sample and the ratio of single, double and multicomponent radio sources is computed based on FIRST radio maps. The 74, 365, 1400, and 4850MHz data of the VLSS, TXS, NVSS, FIRST, and GB6 catalogs are used to analyze the shape of the spectra. 相似文献
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We report the results of optical identification of a sample of RC catalog radio sources with the FIRST and SDSS surveys. For 320 sources identified with NVSS and FIRST objects we perform optical identification with the SDSS survey. When selecting optical candidates we make maximum use of the information about the structure of radio sources as provided by the FIRST survey images. We find optical candidates for about 70% of all radio sources. 相似文献
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Natasha Maddox Paul C. Hewett 《Monthly notices of the Royal Astronomical Society》2006,367(2):717-731
A number of deep, wide-field, near-infrared (NIR) surveys employing new infrared cameras on 4-m class telescopes are about to commence. These surveys have the potential to determine the fraction of luminous dust-obscured quasars that may have eluded surveys undertaken at optical wavelengths. In order to understand the new observations it is essential to make accurate predictions of surface densities and number–redshift relations for unobscured quasars in the NIR based on information from surveys at shorter wavelengths. The accuracy of the predictions depends critically on a number of key components. The commonly used single power-law representation for quasar spectral energy distributions (SEDs) is inadequate and the use of an SED incorporating the upturn in continuum flux at λ∼ 12 000 Å is essential. The presence of quasar host galaxies is particularly important over the rest-frame wavelength interval 8000 < λ < 16 000 Å and we provide an empirical determination of the magnitude distribution of host galaxies using a low-redshift sample of quasars from the Sloan Digital Sky Survey Data Release 3 quasar catalogue. A range of models for the dependence of host galaxy luminosity on quasar luminosity is investigated, along with the implications for the NIR surveys. Even adopting a conservative model for the behaviour of host galaxy luminosity the number counts for shallow surveys in the K band increase by a factor of 2. The degree of morphological selection applied to define candidate quasar samples in the NIR is found to be an important factor in determining the fraction of the quasar population included in such samples. 相似文献
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A. V. Meshcheryakov V. V. Glazkova S. V. Gerasimov I. V. Mashechkin 《Astronomy Letters》2018,44(12):735-753
We present empirical machine learning algorithms for measuring the probabilistic photometric redshifts (photo-z) of X-ray quasars based on the quantile regression of ensembles of decision trees. Relying on the data of present-day photometric sky surveys (e.g., SDSS, GALEX, WISE, UKIDSS, 2MASS, FIRST), the proposed methods allow one to make high-quality photo-z point predictions for extragalactic objects, to estimate the confidence intervals, and to reconstruct the full probability distribution functions for all predictions. The quality of photo-z predictions has been tested on samples of X-ray quasars from the 1RASS and 3XMM DR7 surveys, which have spectroscopic redshift measurements in the SDSS DR14Q catalog. The proposed approaches have shown the following accuracy (the metrics are the normalized median absolute deviation σNMAD and the percentage of outliers n>0.15): σNMAD, n>0.15 = 0.043, 12% (SDSS + WISE), 0.037, 8% (SDSS + WISE + GALEX) and 0.032, 8.6% (SDSS + WISE + GALEX + UKIDSS) on the RASS sample; σNMAD, n>0.15 = 0.054, 13% (SDSS + WISE), 0.045, 7.6% (SDSS + WISE + GALEX), and 0.037, 6.6% (SDSS + WISE + GALEX + UKIDSS) on the 3XMM sample. The presented photo-z algorithms will become an important tool for analyzing the multi-wavelength data on X-ray quasars in the forthcoming Spectrum–Roentgen–Gamma sky survey. 相似文献
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M. G. Revnivtsev A. Kniazev D. I. Karasev L. Berdnikov S. Barway 《Astronomy Letters》2013,39(8):523-531
Increasing the identification completeness of sources from new X-ray sky surveys is a necessary condition for further works on analyzing the formation and long-term evolution of star systems in our Galaxy. Infrared observations of several sources selected from Galactic plane surveys as candidates for low-mass X-ray binaries with the IRSF telescope at the South African Astronomical Observatory are presented. The infrared fluxes have been reliably measured from five of the eight sources (4U 1556-60, 4U 1708-40, AX J165901-4208, IGR J16287-5021, IGR J17350-2045, AX J171922-3703, SAX J1712.6-3739, 4U 1705-32). One of the objects (AX J165901-4208) may be a candidate for symbiotic X-ray binaries, i.e., binaries in which the companion of a relativistic object is a giant star. The distances have been estimated for three sources and the orbital periods have been estimated for two. 相似文献
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The second part of the First Byurakan Survey is aimed at detecting all bright (B < 16.5) UV-excess starlike objects in a large
area of the sky. By comparison with other major surveys such as the ROSA T All Sky Survey, the ROSAT WGACAT catalogue of point
sources, the IRAS survey, the 6cm Green Bank, the 1.4GHz NRAO VLA, and the 92cm Westerbork Northern sky surveys and with the
catalogue of mean UBVdata on stars, we estimate the number of AGNs present in the FBS survey and its completeness. We have made spectroscopic observations
of nine of the most promising FBS candidates. We have found six new QSOs, bringing the total number of known QSOs in this
survey to 42. By comparison with the Bright Quasar Survey, we found that the completeness of this last survey is of the order
of 70% rather than 30–50% as suggested by several authors.
Based party on observations collected at the Observatorie de Haute-Provence (CNRS, France). The APS databases are supported
by the National Foundation, the National Aeronautics and Space Administration, and the University of Minnesota, and are available
at hup:// aps.umn.edu. The Digitized Sky Survey was produced at the Space Telescope Science Institute (STScI) under U.S. Government
Grant NAG W-2166.
Published in Astrofizika, Vol. 42, No. 1, pp. 5–22, January–March, 1999. 相似文献