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Zhang X.-G.,Chinese Academy of Sciences | Zhang X.-G.,Chinese Center for Antarctic Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2013

In this paper, the optical spectra index-luminosity relationship is checked for the well-known 17 individually mapped quasi-stellar objects (QSOs), in order to give one more clearer conclusion on the so far conflicting dependence of the spectral index on the luminosity for an active galactic nucleus (AGN). Unlike the global relationships based on the colour difference (photometry parameters) for samples of AGNs, a more reliable relationship is determined for the multi-epoch observed individually mapped QSOs with no contamination from the host galaxies, the line variabilities and the very different central properties. The final confirmed results are as follows. (i) No strong dependence of the optical spectral index on the continuum luminosity can be found for all 17 QSOs, besides two objects (PG 0026 and PG 1613) that have some weak trends (with 3σ confidence level) for the relationship. In other words, the common expectation that 'AGNs get bluer when they get brighter' is not so common. (ii) There are very different damped intrinsic variability time-scales for the variability modes of the optical spectral index and the continuum emission, through the well-applied damped random walk method for the AGN variability. In other words, there are some different intrinsic mechanisms controlling the variabilities of the optical spectral index and the power-law AGN continuum emission. Therefore, the much weaker dependence of the optical spectral index on the continuum luminosity can be further confirmed. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zhang X.-G.,Chinese Academy of Sciences | Zhang X.-G.,Chinese Center for Antarctic Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2013

In this paper, the properties of the proposed intermediate broad emission line region (BLR) are checked for the mapped AGN PG 0052+251. With the considerations of the apparent effects of the broad He II line on the observed broad Hβ profile, the line parameters (especially the line width and the line flux) of the observed broad Ha and the broad Hβ are carefully determined. Based on the measured line parameters, the model with two broad components applied for each observed broad Balmer line is preferred, and then confirmed by the calculated much different time lags for the inner/intermediate broad components and the corresponding virial black hole mass ratio determined by the properties of the inner and the intermediate broad components. Then, the correlation between the broad line width and the broad line flux is checked for the two broad components: one clearly strong negative correlation for the inner broad component and one positive correlation for the intermediate broad component. The different correlations for the two broad components strongly support the intermediate BLR of PG 0052+251. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zhang X.-G.,Chinese Academy of Sciences | Zhang X.-G.,Chinese Center for Antarctic Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2013

In this paper, we carefully check the correlation between the line width (second moment) and the line flux of the double-peaked broad Ha of the well-known mapped active galactic nucleus (AGN) 3C390.3 in order to show some further distinctions between double-peaked emitters and normal broad-line AGN. Based on the virialization assumption MBH αRBLR × V2(BLR) and the empirical relation RBLR α L~0.5, one strong negative correlation between the line width and the line flux of the double-peaked broad lines should be expected for 3C390.3, such as the negative correlation confirmed for the mapped broad-line object NGC5548, RBLR × V2x(BLR)αL~0.5 ×s2 =constant.Moreover, based on the public spectra around 1995 from the AGN WATCH project for 3C390.3, one reliable positive correlation is found between the line width and the line flux of the double-peaked broadHa. In the context of the proposed theoretical accretion disc model for double-peaked emitters, the unexpected positive correlation can be naturally explained, due to different time delays for the inner and outer parts of the disc-like broad-line region (BLR) of 3C390.3. Moreover, the virialization assumption is checked and found to be still available for 3C390.3. However, the time-varying size of the BLR of 3C390.3 cannot be expected by the empirical relation RBLR α L~0.5. In other words, the mean size of the BLR of 3C390.3 can be estimated by the continuum luminosity (line luminosity), while the continuum emission strengthening leads to the size of BLR decreasing (not increasing) in different moments for 3C390.3. Then, we compared our results of 3C390.3 with the previous results reported in the literature for the other double-peaked emitters, and found that before to clearly correct the effects from disc physical parametersvarying (such as the effects of disc precession) for long-term observed line spectra, it is not so meaningful to discussthe correlation of the line parameters of double-peaked broad lines. Furthermore, due to the probable 'external' ionizing source with so far unclear structures, it is hard to give one conclusion that the positive correlation between the line width and the line flux can be found for all double-peaked emitters, even after the considerations of disc physical parameters varying. However, once one positive correlation of broad-line parameters is found, the accretion disc origination of the broad line should be considered first. © 2012 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zhang X.-G.,Chinese Academy of Sciences | Zhang X.-G.,Chinese Center for Antarctic Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2014

This is the first paper in a dedicated series to study the properties of the optically-selected broad-line-region-less (BLR-less) active galactic nuclei (AGNs; with no-hidden central broad emission line regions). We carried out a systematic search for the BLR-less AGNs through the Sloan Digital Sky Survey Legacy Survey (SDSS Stripe82 Database). Based on the spectral decomposition results for all the 136 676 spectroscopic objects (galaxies and quasars) with redshift less than 0.35 covered by the SDSS Stripe82 region, our spectroscopic sample for the BLR-less AGNs includes 22 693 pure narrow line objects without broad emission lines but with apparent AGN continuum emission RAGN > 0.3 and apparent stellar lights Rssp > 0.3. Then, using the properties of the photometry magnitude RMS (RMS) and Pearson's coefficients (R1, 2) between two different SDSS band light curves: RMSk 3 × RMSMk and R1, 2 > ∼0.8, the final 281 pure narrow line objects with true photometry variabilities are our selected reliable candidates for the BLR-less AGNs. The selected candidates with higher confidence levels not only have the expected spectral features of the BLR-less AGNs, but also show significant true photometry variabilities. The reported sample enlarges at least four times the current sample of the BLR-less AGNs, and will provide more reliable information to explain the lack of the BLRs of AGNs in our following studies. © 2013 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.


Wei J.-J.,Chinese Academy of Sciences | Wu X.-F.,Chinese Academy of Sciences | Wu X.-F.,Chinese Center for Antarctic Astronomy | Wu X.-F.,Nanjing University | Melia F.,University of Arizona
Astrophysical Journal | Year: 2013

In this paper, we continue to build support for the proposal to use gamma-ray bursts (GRBs) as standard candles in constructing the Hubble diagram at redshifts beyond the current reach of Type Ia supernova observations. We confirm that correlations among certain spectral and light-curve features can indeed be used as luminosity indicators, and demonstrate from the most up-to-date GRB sample appropriate for this work that the CDM model optimized with these data is characterized by parameter values consistent with those in the concordance model. Specifically, we find that (ωm, ωδ ≈ (0.25+0.05 0.06, 0.75 +0.06 0.05), which are consistent, to within 1, with (0.29, 0.71) obtained from the 9 yr Wilkinson Microwave Anisotropy Probe data. We also carry out a comparative analysis between ta;CDM and the Rh = ct universe and find that the optimal δCDM model fits the GRB Hubble diagram with a reduced ?2 dof ≈ 2.26, whereas the fit using Rh = ct results in a ?2 dof ≈ 2.14. In both cases, about 20% of the events lie at least 2? away from the best-fit curves, suggesting that either some contamination by non-standard GRB luminosities is unavoidable or that the errors and intrinsic scatter associated with the data are being underestimated. With these optimized fits, we use three statistical toolsthe Akaike information criterion, the Kullback information criterion, and the Bayes information criterionto show that, based on the GRB Hubble diagram, the likelihood of Rh = ct being closer to the correct model is ∼85%96%, compared to ∼4%15% for δCDM. © 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


Zhang X.-G.,Chinese Academy of Sciences | Zhang X.-G.,Chinese Center for Antarctic Astronomy
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

In this Letter, under the widely accepted theoretical accretion disc model for the double-peaked emitter 3C 390.3, the extended disc-like broad-line region can be well split into 10 rings, and then the time lags between the lines from the rings and the continuum emission are estimated, based on the observed spectra around 1995. We can find one very strong correlation between the determined time lags (in units of light-day) and the flux-weighted radii (in units of RG) of the rings, which is well consistent with the expected results through the theoretical accretion disc model. Moreover, through the strong correlation, the black hole masses of 3C 390.3 are independently estimated as 109M⊙, the same as the reported black hole masses in the literature. The consistencies provide further evidence to strongly support the accretion disc origination of the double-peaked broad Balmer lines of 3C 390.3. © 2013 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zhang X.-G.,Chinese Academy of Sciences | Zhang X.-G.,Chinese Center for Antarctic Astronomy
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

In this letter, we report on the positive correlations between the broad-line width and broadline flux for the broad Balmer lines of the active galactic nucleus (AGN) PG 1613+658, which has been observed for a long time. Rather than the expected negative correlations that come with the widely accepted virialization assumption for AGN broad emission-line regions (BLRs), the positive correlations indicate very different BLR structures of PG 1613+658 from the commonly considered BLR structures that are dominated by the equilibrium between radiation pressure and gas pressure. Therefore, it is preferable to assume that the observed broad single-peaked optical Balmer lines of PG 1613+658 originate from the accretion disc, because the mainly gravity-dominated disc-like BLRs with radial structures have few effects from radiation pressure. © 2014 The Author.


Zhang X.-G.,Chinese Academy of Sciences | Zhang X.-G.,Chinese Center for Antarctic Astronomy
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

In this Letter, we first report one unique object SDSS J0832+0643 with particular features of narrow Balmer emission lines: double-peaked narrow Hα but single-peaked narrow Hβ. The particular features cannot be expected by currently proposed kinematic models for doublepeaked narrow emission lines, because the proposed kinematic models lead to similar line profiles of narrow Balmer emission lines. However, due to radiative transfer effects, the nonkinematic model can be naturally applied to well explain the particular features of narrow Balmer emission lines: larger optical depth in Hα than 10 leads to observed double-peaked narrow Hα, but smaller optical depth in Hβ around 2 leads to observed single-peaked narrow Hβ. Therefore, SDSS J0832+0643 can be used as strong evidence to support the non-kinematic model for double-peaked narrow emission lines. © 2015 The Author.


Yuan X.,Nanjing Institute of Technology | Yuan X.,Chinese Academy of Sciences | Yuan X.,Chinese Center for Antarctic Astronomy | Su D.-Q.,Nanjing Institute of Technology | Su D.-Q.,Nanjing University
Monthly Notices of the Royal Astronomical Society | Year: 2012

Dome A is the highest point on the Antarctic Plateau, and the Chinese Expedition Team first arrived here in 2005 January. It is an excellent site for astronomical observations. The first-generation Chinese Antarctic optical telescope CSTAR has been operating on Dome A since 2008 January. The second-generation Chinese telescopes known as the Three Antarctic Survey Telescopes (AST3) are currently being developed. AST3 includes three telescopes matched respectively with G-, R- and I-band filters. Each telescope is a catadioptric optical telescope with an entrance pupil diameter of 500 mm, an f-ratio of 3.73 and a field of view of 414. The optical system of the AST3 consists of a transparent aspherical plate, an aspherical primary mirror and a spherical refractive corrector with a filter before the focal plane. The main features of the AST3 are the following: good image quality, a planar focal plane, reduced atmospheric dispersion, an absence of distortion and a compact structure. The main scientific goal of the AST3 is to survey the sky. In 2012 January, the first telescope of the AST3 was successfully installed on Dome A. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Liu R.-Y.,Nanjing University | Liu R.-Y.,Max Planck Institute for Nuclear Physics | Wang X.-Y.,Nanjing University | Wu X.-F.,Chinese Academy of Sciences | And 2 more authors.
Astrophysical Journal Letters | Year: 2013

High-energy photons (>100 MeV) are detected by the Fermi/Large Area Telescope from GRB 130427A up to almost one day after the burst, with an extra hard spectral component discovered in the high-energy afterglow. We show that this hard spectral component arises from afterglow synchrotron self-Compton (SSC) emission. This scenario can explain the origin of >10 GeV photons detected up to 30, 000 s after the burst, which would be difficult to explain via synchrotron radiation due to the limited maximum synchrotron photon energy. The lower energy multi-wavelength afterglow data can be fitted simultaneously by the afterglow synchrotron emission. The implication of detecting the SSC emission for the circumburst environment is discussed. © 2013. The American Astronomical Society. All rights reserved..

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