共查询到18条相似文献，搜索用时 62 毫秒
1.
Ya-Di Xu Xin-Wu Cao 《中国天文和天体物理学报》2009,9(4)
It was found that advection-dominated accretion flow (ADAF)+thin disk model calculations can reproduce the observed spectral energy distributions (SEDs) of two low- luminosity active galactic nuclei (AGNs), provided they are accreting at ～ 0.01 - 0.03 Eddington rates and the thin disks are truncated to ADAFs at～ 100Rs (Rs is the Schwarzschild radius) for M81 and NGC 4579 (Quataert et al. 1999). However, the black hole masses adopted in their work are about one order of magnitude lower than recent measurements on these two sources. Adopting the well estimated black hole masses, our ADAF+thin disk model calculations can reproduce the observed SEDs of these two low- luminosity AGNs, if the black hole is accreting at 2.5 × 10-4 Eddington rates with the thin disk truncated at Rtr = 120Rs for M81 ((m) = 3.3 × 10-3 and Rtr = 80Rs are required for NGC 4579). The transition zones with temperature from the thin disk with 104 - 105 to～109 - 1010 K in the ADAF will inevitably emit thermal X-ray lines, which provides a useful diagnosis of their physical properties. The observed widths of the thermal X-ray iron lines at(～)6.8 keV are consistent with Doppler broadening by Keplerian motion of the gases in the transition zones at～100Rs. We use the structure of the transition zone between the ADAF and the thin disk derived by assuming the turbulent diffusive heat mechanism to calculate their thermal X-ray line emission with the standard software package Astrophysical Plasma Emission Code (APEC). Comparing them with the equivalent widths of the observed thermal X-ray iron lines in these two sources, we find that the turbulent diffusive heat mechanism seems to be unable to reproduce the ob- served thermal X-ray line emission. The test of the evaporation model for the accretion mode transition with the observed thermal X-ray line emission is briefly discussed. 相似文献
2.
Min-Zhi Kong Xue-Bing Wu Jin-Lin Han Yu-Feng Mao National Astronomical Observatories Chinese Academy of Sciences Beijing Department of Astronomy Peking University Beijing 《中国天文和天体物理学报》2004,4(6):518-526
Using the archived optical spectra of NGC 5548 between 1989 and 2001, we derived the optical spectral index by fitting the spectra in wavelength windows unaffected by strong emission lines. We found that the index is anti-correlated with the continuum luminosity at 5100 A with a correlation coefficient of -0.8. Based on the standard thin accretion disk model, we investigated whether the correlation is related to the variations of the dimensionless accretion rate m (mass accretion rate in Eddington unit), or the inner radius of the accretion disk Rin, or both. The correlation can be modeled well using a co-variable mode of Rin/Rs = 12.5m-0.8 (Rs is Schwarzschild radius). As luminosity increases, m increases from 0.05 to 0.16 and at the same time Rin decreases from 133.9.RS to 55.5.RS, consistent with the prediction for a transition radius within which an ADAF structure exists. We concluded that the change of both inner accretion radius and the dimensionless accretion rate are key factors for the variation 相似文献
3.
Guang-Zhong Xie Luo-En Chen Huai-Zhen Li Li-Sheng Mao Hong Dai Zhao-Hua Xie Li Ma Shu-Bai Zhou National Astronomical Observatories Yunnan Observatory Chinese Academy of Science Kunming Yunnan Astrophysics Center Yunnan University Kunming Physics Department Yunnan Normal University Kunming Physics Department Yuxi Normal College Yuxi Graduate University of Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(5):463-470
Black hole mass is one of the fundamental physical parameters of active galactic nuclei (AGNs), for which many methods of estimation have been proposed. One set of methods assumes that the broad-line region (BLR) is gravitationally bound by the central black hole potential, so the black hole mass can be estimated from the orbital radius and the Doppler velocity. Another set of methods assumes the observed variability timescale is determined by the orbital timescale near the innermost stable orbit around the Schwarzschild black hole or the Kerr black hole, or by the characteristic timescale of the accretion disk. We collect a sample of 21 AGNs, for which the minimum variability timescales have been obtained and their black hole masses (Mσ) have been well estimated from the stellar velocity dispersion or the BLR size-luminosity relation. Using the minimum variability timescales we estimated the black hole masses for 21 objects by the three different methods, the results are denoted by Ms, Mk and Md, respectively. We compared each of them with Mσindividually and found that: (1) using the minimum variability timescale with the Kerr black hole theory leads to small differences between Mσand Mk, none exceeding one order of magnitude, and the mean difference between them is about 0.53 dex; (2) using the minimum variability timescale with the Schwarzschild black hole theory leads to somewhat larger difference between Mσand Ms: larger than one order of magnitude for 6 of the 21 sources, and the mean difference is 0.74 dex; (3) using the minimum variability timescale with the accretion disk theory leads to much larger differences between Mσand Md, for 13 of the 21 sources the differences are larger than two orders of magnitude; and the mean difference is as high as about 2.01 dex. 相似文献
4.
ASCA observations of the two Type Ⅱ AGNs,NGC7314 and NGC 7582,show clear variations in the broad X-ray band(0.4-10keV)on short timescales-10^4s.Spectral analysis indicates that they bot have an absorbed hard X-ray component and an unabsorbed soft“excess” component.To clarify the origin of the latter,we made a cross-correlation analysis of the two components.The results show that,for NGC7314,the soft X-ray variability is proportional to that of the hard X-ray component.This indicates that the active nucleus of NGC 7314 must be partially covered and so the soft emission is a “leaking” of the variable hard component.For NGC 7582,there is no detectable variability in the soft component, although there is a definite one in the hard component.This indicates that the variable nucleus of NGC 7582 must be fully blocked by absorbing matter,and the soft emission is most likely the scattered component predicted by the AGN unified model. 相似文献
5.
Bing Luo Ji-Yao Chen Zhong-Li Zhang Yu Wang Jing-Ying Wang Hai-Guang Xu 《中国天文和天体物理学报》2007,7(3):335-344
Using Chandra ACIS S3 data we studied the X-ray properties of low-and high- mass X-ray binary populations in the nearby spiral galaxy NGC 5055. A total of 43 X-ray point sources were detected within two effective radii, with 31 sources located on the disk and the rest 12 sources in the bulge. The resolved point sources dominate the X-ray emission of the galaxy, accounting for about 80% of the total counts in 0.3–10keV. From spectral fittings we calculated the 0.3–10.0keV luminosities of all the detected X-ray point sources and found that they span a wide range from a few times 1037 erg s-1 to over 1039 erg s-1. After compensating for incompleteness at the low luminosity end, we found that the corrected XLF of the bulge populationis well fitted with a brokenpower-law with a break at 1.57 - 00..2210× 1038 erg s-1, while the profile of the disk population’s XLF agrees with a single power- law distribution of slope 0.93 -00..0076. The disk population is significantly richer at >～ 2 × 1038 erg s-1 than the bulge population, indicating that the disk may have undergonerelatively recent, strong starbursts that significantly increased the HMXB population, although ongoing starbursts are also observed in the nuclear region. Similar XLF profiles of the bulge and disk populations were found in M81. However, in most other spiral galaxies different patterns of spatial variation of the XLF profiles from the bulge to the disk have been observed, indicating that the star formation and evolution history may be more complex than we have expected. 相似文献
6.
Low mass black hole binaries are generally transient sources and spend most of their time in the quiescent state. It is believed that the inner accretion flow in the quiescent state is in the form of advection dominated accretion flow and the cold outer accretion disk is truncated far away from the central black hole. During the onset of an outburst, the disk gradually extends towards the central black hole.However, the observational evidence for this general picture is indirect at best. Here we present the results of a study performed to understand the variation of the inner disk radius during the early phase of an outburst. We investigated the variation of the inner disk radius during the 2010 outburst of the black hole candidate MAXI J1659-152 using the method of simultaneous spectral fitting. We found that the inner edge of the disk is truncated at a large radius in the beginning of the outburst when the source was in the hard state. We found a systematic decrease in the inner disk radius as the outburst progressed. We also estimated an upper limit on the mass of the black hole to be 8.1 ± 2.9 M within the uncertainty of the distance and inclination angle. 相似文献
7.
Xi-Wei Liu Xiang-Dong Li 《中国天文和天体物理学报》2007,7(3):389-396
Assuming a naive star formation history, we construct synthetic X-ray source pop- ulations, using a population synthesis code, for comparison with the observed X-ray lumi- nosity function (XLF) of the interacting galaxies NGC 4038/4039. We have included high- and intermediate-mass X-ray binaries, young rotation-powered pulsars and fallback disk-fed black holes in modeling the bright X-ray sources detected. We find that the majority of the X-ray sources are likely to be intermediate-mass X-ray binaries, but for typical binary evolu- tion parameters, the predicted XLF seems to be steeper than observed. We note that the shape of the XLFs depends critically on the existence of XLF break for young populations, and suggest super-Eddington accretion luminosities or the existence of intermediate-mass black holes to account for the high luminosity end and the slope of the XLF in NGC 4038/4039. 相似文献
8.
《天文和天体物理学研究(英文版)》2019,(12)
We perform a search for gravitational waves(GWs) from several supermassive binary black hole(SMBBH) candidates(NGC 5548, Mrk 231, OJ 287, PG 1302–102, NGC 4151, Ark 120 and 3C 66B) in long-term timing observations of the pulsar PSR J1909-3744 obtained using the Parkes radio telescope.No statistically significant signals were found. We constrain the chirp masses of those SMBBH candidates and find the chirp mass of NGC 5548 and 3C 66B to be less than 2.4 × 10~9 M_⊙ and 2.5 × 10~9 M_⊙(with 95% confidence), respectively. Our upper limits remain a factor of 3 to 370 above the likely chirp masses for these candidates as estimated from other approaches. The observations processed here provide upper limits on the GW strain amplitude that improve upon the results from the first Parkes Pulsar Timing Array data release by a factor of 2 to 7. We investigate how information about the orbital parameters can help to improve the search sensitivity for individual SMBBH systems. Finally, we show that these limits are insensitive to uncertainties in the Solar System ephemeris model. 相似文献
9.
Hui Dong Sui-Jian Xue Cheng Li Fu-Zhen Cheng Center for Astrophysics University of Science Technology of China Hefei National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(5):427-439
Chandra observations of the Seyfert-2 galaxies NGC 2110 and NGC 7582 are presented. With the superb spatial resolution of Chandra we found that in NGC 7582 the soft (≤2 keV) and hard (2-10 keV) X-rays are emitted in different regions, consistent with the report by Xue et al. By comparing the present X-ray data with the previous infrared data, we determined that the soft X-ray region is the site of starburst activities. We found no significant temporal variations during our observations. We confirm the previous finding that NGC 2110 and NGC 7582 are flat-spectrum sources. We argue that the flat spectra may result from a cold absorbing material such as envisaged in the “dual absorbed” model. Strong Fe Kα emission feature is detected in 6-7keV. Its equivalent width is so large that it cannot be reproduced by using the Galactic column density of - 10^22 cm^-2. 相似文献
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Xiang-Hua Zou Sui-Jian Xue Department of Astronomy Peking University Beijing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2002,(4)
ASCA observations of the two Type II AGNs, NGC 7314 and NGC 7582, show clear variations in the broad X-ray band (0.4-10keV) on short timescales - 104s. Spectral analysis indicates that they both have an absorbed hard X-ray component and an unabsorbed soft "excess" component. To clarify the origin of the latter, we made a cross-correlation analysis of the two components. The results show that, for NGC 7314, the soft X-ray variability is proportional to that of the hard X-ray component. This indicates that the active nucleus of NGC 7314 must be partially covered and so the soft emission is a "leaking" of the variable hard component. For NGC 7582, there is no detectable variability in the soft component, although there is a definite one in the hard component. This indicates that the variable nucleus of NGC 7582 must be fully blocked by absorbing matter, and the soft emission is most likely the scattered component predicted by the AGN unified model. 相似文献
13.
Hui Men Jin-Lin HanNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(1):49-56
We present total intensity maps of the galaxy NGC 2997 at frequencies 1435.1MHz (λ21cm) and 1652.4MHz (λ18cm) observed with the Very Large Array (VLA). The high spatial resolution allows us to distinguish two dominant arms. Using multi-frequency data, we separate the thermal and non-thermal contributions to the radio emission. The thermal emission is about 35% of the total emission at λ3 cm. We use it to estimate a space-averaged thermal 相似文献
14.
Stellar photometry of images from the ACS and WFPC2 cameras on the Hubble Space Telescope (HST) is used to study the star composition and spatial distribution of stars in three edge-on visible spiral galaxies: NGC 891, NGC 4144, and NGC 4244. Measurements of the surface number density of old stars revealed two stellar subsystems in these galaxies: a thick disk and a halo. The boundaries of these subsystems, which consist mainly of red giants, are determined from the change in the gradient of the number density of the stars. The halos are flattened at the poles of the galaxies and extend to distances of 8–25 kpc from the planes of the galaxies. The present results on the number density distribution of stars with different ages perpendicular to the planes of these galaxies make it possible to improve our model for the stellar structure of spiral galaxies. The distances to these galaxies are calculated using a determination of the tip of the red giant branches (the TRGB method): D = 9.82 Mpc (NGC 891), D = 7.24 Mpc (NGC 4144), and D = 4.29 Mpc (NGC 4244).__________Translated from Astrofizika, Vol. 48, No. 2, pp. 261–280 (May 2005). 相似文献
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We present UBVI surface photometry over a 20.5' × 20.5' area of the late-type spiral galaxy NGC 300. We have derived isophotal maps, surface brightness profiles, ellipticity profiles, position angle profiles, and color profiles. By merging our I-band measurements with those of Boker et al. based on Hubble Space Telescope observations, we have obtained combined I-band surface brightness profiles for the region 0.02" < r < 500" and have decomposed the profiles into three components: a nucleus, a bulge, and an exponential disk. 相似文献
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