G. Z. Xie

Yunnan University, Kunming, Yunnan, China

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Publications (119)276.11 Total impact

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    ABSTRACT: In this paper, we have collected the available observation data of BL Lac S5 0716+714 in I-band from published literature during 1994 to 2000. The light curve shows S5 0716+714 is very active and very complicated non-sinusoidal variations. We studied its medium-timescale periodicity using the Jurkevich and power spectrum method to search for the possible medium-timescale periods and found that one possible medium-timescale periodic with a period of around 14±0.1 day is obtained for S5 0716+714. It is interesting to note that these results are in good agreement with the previous results by Impey et al. (2000) and Qian et al. (2002), and this work provides a new analysis and evidence of the medium-timescale periodicity in BL Lac S5 0716+714. The helical jet model seems to be more reasonable for explaining our results than other models.
    International Journal of Modern Physics D 01/2012; 13(04). DOI:10.1142/S0218271804004773 · 1.42 Impact Factor
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    ABSTRACT: The observation data in the B band for BL Lacerate object PKS 0735+178 during 1970–1998 from twenty two publications have been compiled into a light curve. The light curve shows that PKS 0735+178 is very active and exhibits very complicated non-sinusoidal variations. Using both Jurkevich's method and Power spectrum method to analyze these data we have found two periods of 5.26±0.98 years and 1.24±0.05 years for the outbursts in PKS 0735+178. It is of interest to note that the results of the two methods are the same (almost). In addition, these values are in good agreement with the results found by Smith et al.47 and Webb et al.61 We also apply the binary black hole model to explain the central structure of this object and obtain the masses of the primary and secondary black holes are 1.7×109M⊙ and 2.88×107M⊙ respectively. It should be monitored in future to obtain more data for further analysis to test the hypothesis.
    International Journal of Modern Physics D 01/2012; 13(04). DOI:10.1142/S0218271804004694 · 1.42 Impact Factor
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    ABSTRACT: In this paper, we introduce a new composite spectral indices αγxγ = αxγ - αγ, and prove , that means αγxγ is intrinsic. We plot a αxox - αγxγ diagram for 25 Gev γ-ray blazars for which αx and αγ have been provided in the literature, where αxox = αox - αx which was introduced by Sambruna et al. (1996) and proved that it is intrinsic by our previous paper (Xie et al. 2001). Using this new composite color–color (αxox - αγxγ) diagram, we investigated the nature of the HBLs–LBLs relationship, and the BL Lacs–FSRQs relationship, in high-energy emission. The results show that the spectral energy distributions of three subclasses of Gev γ-ray loud blazars are different, but essentially continuous: HBLs and FSRQs occupy separated regions while LBLs bridge the gap between HBLs and FSRQs. The results are consistent with that derived from a low energy color–color(αxox - αoro) diagram by Sambruna et al. (1996) and Xie et al. (2001). However, on the αox - αxγ diagram, FSRQs, LBLs and HBLs occupy same region. Because both αγxγ and αxox are intrinsic, thus, the new connection among HBLs, LBLs and FSRQs obtained by us is intrinsic.
    International Journal of Modern Physics D 01/2012; 12(05). DOI:10.1142/S0218271803003451 · 1.42 Impact Factor
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    ABSTRACT: We present the results of the monitoring of a sample of 5 HBLs in the B, V and R bands during 2003–2008. All sources in our monitoring project show significant rapid optical variations, except 1ES 1959+650, however; for 1ES 1959+650, the gamma-ray variability on a timescale of ∼7hours has been observed by Holder et al. (Astrophys. J. 583:L9, 2003). Using these variability timescales, we estimate the black hole masses for each source with the Kerr black hole theory. KeywordsBlack hole physics-Galaxies: active-Galaxies: nuclei-Galaxies: photometry-BL Lac objects: general
    Astrophysics and Space Science 05/2010; 327(1):35-58. DOI:10.1007/s10509-010-0268-3 · 2.40 Impact Factor
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    ABSTRACT: We have analyzed the radio light curves of the Seyfert galaxy III Zw 2 at 22 and 37 GHz taken from the database of Metsähovi Radio Observatory, and found evidence of quasi-periodic activity. The light curves show great activity, with very complicated non-sinusoidal variations. Period of was consistently identified by three methods: the Jurkevich method, the power spectrum intensity estimation method and the discrete correlation function method. The variability period of about 5.14 yr in III Zw 2 is caused most likely by the helical motion of the jet.
    New Astronomy 02/2010; 15(2):254-259. DOI:10.1016/j.newast.2009.08.001 · 1.24 Impact Factor
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    ABSTRACT: We complied the optical, X-ray, and γ-ray data for 54 Fermi blazars and studied the relationship between the broadband spectral index α ox and α xγ, as well as the relationship between the intrinsic composite spectral indices α xox and αγxγ for this sample. The relationship between α xox and αγxγ reveals that flat spectrum radio quasars and low-energy peaked BL Lacertae follow a continuous trend, which is consistent with previous results, whereas high-energy peaked BL Lacertae follow a separate distinct trend. Even so, a unified scheme is also revealed from α xox -αγxγ diagram when all three subclasses of blazars are considered.
    The Astrophysical Journal 01/2010; 709(2):1407. DOI:10.1088/0004-637X/709/2/1407 · 6.28 Impact Factor
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    ABSTRACT: We have analyzed the light curves of 3C 279 at 22 GHz, 37 GHz, optical R band, and X-ray (2-10 KeV), and found evidence of quasi-periodic outbusts. The light curves show that 3C 279 is an extremely active object. A period of P=130.6±1.3 days was consistently confirmed by three methods: the power-spectrum method, the discrete correlation function (DCF) method, and the Jurkevich method. Based on the relationship between observed period P and the precession period P given by Rieger and our result, the precession period of jet in 3C 279 is P~=29.6 yr, which is completely consistent with the precession period of jet of about 30 yr obtained by Carrara et al.. This suggests that there is a precession jet in 3C 279 and the variability period of about 130.6 days that we obtained is most likely caused by the helical motion of the jet.
    Publications of the Astronomical Society of the Pacific 11/2009; 121:1172-1179. DOI:10.1086/648433 · 3.23 Impact Factor
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    ABSTRACT: We present optical monitoring between 1994 February and 1997 December of 10 γ-ray-loud blazars included in our blazar monitoring program. Most of the monitored objects show significant rapid variations. The typical minimum variability timescale in the optical range is about 1 hour. We have analyzed the relationships between optical variability and γ-ray variability, and discussed theoretical models for the γ-ray-loud blazar emission.
    The Astrophysical Journal 01/2009; 522(2):846. DOI:10.1086/307673 · 6.28 Impact Factor
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    ABSTRACT: The ROSAT All-Sky Survey-Green Bank (RGB) BL Lac object sample presented by Laurent-Muehleisen et al. includes not only interesting intermediate but also extreme HBL and LBL sources. These unique characteristics make it possible to unambiguously address the question of how HBLs and LBLs are related. In this paper, we study the relations between the radio-X-ray spectral index (αrx) and each of the luminosities (Lr, Lo, Lx), as well as the relation between the X-ray spectral index (αx) and the radio luminosity (Lr) for this sample. Our analysis results indicate that (1) plots of (αrx, Li) (i denotes r, o, or x) all exhibit the continuity of αrx; (2) of 71 low-Lr RGB BL Lac objects (L5 GHz < 1025 W Hz-1), 24% have αrx steeper than 0.75, while 79% are distributed in the region 0.6 < αrx < 0.9 and have such a broad scatter in αrx that αrx can range from 0.55 to 0.8 for any given value of Lr; (3) of 60 low-Lr RGB BL Lac objects (with αx available), 20% have αx flatter than 1, and no correlation is present for Lr versus αx. In addition, no correlation is found between Lo and αrx for the RGB BL Lac sample. These characteristics seem inconsistent with those derived from the earlier classic combined surveys. From our analysis, however, we also found that (1) there is a significant anticorrelation for Lx versus αrx, which agrees with that reported by Mei et al., and (2) more importantly, αrx is well correlated with Lr, which is consistent with the result expected in the blazar sequence but in contradiction with that derived from the DXRBS sample. All of these seemingly odd results show the importance of sampling enough parameter space in order to obtain an unbiased view or model of blazar properties.
    The Astrophysical Journal 12/2008; 637(2):711. DOI:10.1086/498439 · 6.28 Impact Factor
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    ABSTRACT: In this paper we report a brief description of 13 γ-ray-loud blazars as the second batch of the results of our blazar monitoring program. Six of the monitored objects show significant rapid variations. We found the typical minimum variability timescale to be about 1 hr. We have analyzed the relationships between optical variability and γ-ray variability and found that during 1995-1996 the TeV γ-ray emission of Mrk 501 correlated to its optical emission, based on our monitoring data in the optical band. This result will provide a strong constraint to the emission models.
    The Astrophysical Journal 12/2008; 548(1):200. DOI:10.1086/318670 · 6.28 Impact Factor
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    ABSTRACT: We have analyzed the radio light curves of PKS 1510-089 at 37 and 22 GHz from 1990 to 2005 taken from the database of the Metsähovi Radio Observatory, and find evidence of quasi-periodic outbursts. The light curves show great activity with very complicated non-sinusoidal variations. Using Jurkervich's method, the power spectrum method, and the discrete autocorrelation function to analyze these data, we have found two periods of p 1 = 0.92 ± 0.04 yr and p 2 = 1.82 ± 0.12 yr for the outbursts in PKS 1510-089. It is interesting to note that the results for two frequencies and three methods are almost the same and p 2 2p 1. In addition, these results are in good agreement with the periodic deep flux minima of 1.84 ± 0.1 yr (half period ~ 0.92 ± 0.03 yr) observed by us and other authors in the optical band in 2002, 2004, and 2005.
    The Astronomical Journal 05/2008; 135(6):2212. DOI:10.1088/0004-6256/135/6/2212 · 4.05 Impact Factor
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    T. F. Yi, G. Z. Xie
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    ABSTRACT: We study the correlations of the flux of the broad-line emission ($F_{BLR}$) with the X-ray emission flux, optical emission flux at 5500 \AA and radio emission flux at 5 GHz, respectively, for a large sample of 50 Blazars (39 flat-spectrum radio quasars (FSRQs) and 11 BL Lac objects). Our main results are as follows. There are very strong correlations between $F_{BLR}$ and $F_{X}$ and between $L_{BLR}$ and $L_{X}$ in both states for 39 FSRQs and the slopes of the linear regression equations are almost equal to 1. There are weak correlations between $F_{BLR}$ and $F_{X}$ and between $L_{BLR}$ and $L_{X}$ for 11 BL Lac objects in both states, and the slopes of the linear regression equations are close to 1. There are significant correlations between $F_{BLR}$ and $F_{X}$ and between $L_{BLR}$ and $L_{X}$ for 50 blazars in both states, the slopes of both the linear regression equations are also close to 1. These results support a close link between relativistic jets and accretion on to the central Kerr black hole. On the other hand, we find that BL Lac objects have low accretion efficiency $\eta$, whereas FSRQs have high accretion efficiency $\eta$. The unified model of FSRQs and BL Lac objects is also discussed.
    Publications- Astronomical Society of Japan 04/2008; DOI:10.1093/pasj/60.2.161 · 2.01 Impact Factor
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    ABSTRACT: We compile a sample of 13 BL Lac objects for which rapid optical variabilities are reliably established and luminosities of the nuclei and the host galaxies have been well observed by the Hubble Space Telescope (HST). We present a new method for estimating the masses of the supermassive black holes (SMBHs) at the centers of these objects using the rapid optical variability, and find that the masses of the SMBHs range from 107.42 to 109.19 M. This mass range is quite similar to that of dark compact objects in galaxies. To further investigate the reliability of our method, we also compile another sample with nine high-energy γ-ray emission sources of BL Lac objects and obtain the masses for the SMBHs in these objects using the Dermer & Gehrels method. We find that the masses derived from these two methods are quite similar. These results strongly imply that the estimation of masses of SMBHs by rapid optical variability is reliable. We examine the correlations of the masses with the luminosities of the nuclei and the host galaxies observed by HST, and find that the masses are significantly correlated with the luminosities of the nuclei, but not correlated with the luminosities of host galaxies at all. In addition, we examine the relation between the observed minimal timescale of variation and the bolometric luminosities of the objects. We find that they obey the Abromowicz & Nobili relation. These results possibly imply that the luminosities of the nuclei are produced by accretion of the central SMBHs.
    The Astronomical Journal 12/2007; 123(5):2352. DOI:10.1086/339974 · 4.05 Impact Factor
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    ABSTRACT: We compiled a sample of 16 flat-spectrum radio quasars (FSRQs), 8 BL Lac objects, and 15 Fanaroff-Riley (FR) I and FR II radio galaxies, for which the intrinsic Eddington ratios and broad-line luminosities are available. In the diagram of the intrinsic Eddington ratio-broad-line luminosity relation, FSRQs are found in the high broad-line luminosity, high intrinsic Eddington ratio region, while BL Lac objects, as well as FR I and FR II radio galaxies, are found in the low broad-line luminosity, low intrinsic Eddington ratio region. In addition, the intrinsic Eddington ratios are strongly correlated with the broad-line luminosities and also with the intrinsic bolometric luminosities, but the correlation with the broad-line luminosities is better. Thus, the broad-line luminosity, rather than the intrinsic bolometric luminosity, should be used as a fundamental parameter of the unified scheme and evolution of active galactic nuclei. On the other hand, we analyze the theory proposed by Czerny and coworkers that the formation of the broad-line region (BLR) is intrinsically connected to the existence of a cold accretion disk. Our studies support that BLR formation is intimately connected with the cold disk. Thus, our results provide solid experimental evidence for the theory that has been proposed by Czerny and coworkers.
    The Astronomical Journal 12/2007; 133(5):2187. DOI:10.1086/511769 · 4.05 Impact Factor
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    G. Z. Xie, H. Dai, and S. B. Zhou
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    ABSTRACT: For a large sample of quasi-simultaneous spectra of blazars from radio to far-infrared wavelengths, we study the correlations of the luminosity of the broad-line emission (LBLR) with the radio core luminosity (L) and the extended radio luminosity (PE). A strong correlation between log LBLR and log L is found for 48 blazars, and the slope of the linear regression equation is close to 1. Our results support the hypothesis that blazar jets are powered by energy extraction from a rapidly spinning Kerr black hole through the magnetic field provided by the accretion disk. Using partial correlation regression analysis for the same sample, we find that the linear correlation coefficient between log LBLR and log L is stronger with the effect of the redshift excluded, and the linear correlation coefficient between log LBLR and log PE is also significant. The results seem to show that the coupling of the jet and accretion disk is very tight, so that LBLR also correlates significantly with extended radio luminosity.
    The Astronomical Journal 12/2007; 134(4):1464. DOI:10.1086/521552 · 4.05 Impact Factor
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    ABSTRACT: A sample of 39 blazars each with a well-established rapid variability timescale and bolometric luminosity has been compiled from the literature. Based on the assumption that central supermassive black holes (SMBHs) are Kerr black holes, the upper limits of the SMBHs were estimated. The masses ranged from 107.2 to 109.4 M, showing a distribution of three subclasses: massive flat-spectrum radio quasars (FSRQs) and smaller mass BL Lac objects occupying separate regions, while medium-mass FSRQs and BL Lac objects bridge the gap. We found that the mass–intrinsic luminosity relations for FSRQs and BL Lac objects are the same. Analysis reveals a relationship of log(Lin/L) = 1.225 log(M/M) + 1.500, which mimics a relationship found in the main sequence. We found that the intrinsic accretion rates are quite different between FSRQs and BL Lac objects. The diagram of the intrinsic accretion rate–luminosity relation shows that FSRQs occur in the earlier, high-luminosity, violent phase of the galactic evolution sequence, while BL Lac objects occur in the low-luminosity, late phase of the galactic evolution sequence. Of note is that the results of the mass-luminosity relation of blazars are consistent with the accretion rate–luminosity relation, and together they prove that active galactic nuclei evolve from FSRQs to BL Lac objects. The evolution diagram of blazars derived in this paper seems to be a Hertzsprung-Russell diagram of star evolution.
    The Astronomical Journal 12/2007; 127(1):53. DOI:10.1086/380218 · 4.05 Impact Factor
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    ABSTRACT: We have spectrophotometrically observed a sample of five optically violently variable quasars, for which short-timescale optical variabilities have been observed during our optical monitoring campaign since 1994. Using the relationship between black hole masses and optical continuum luminosity at the rest wavelength of 5100 Å, we derived the central black hole masses, MBH. We also estimated the relevant black hole masses, MH, using rapid-variability timescales and our new formula for black hole mass estimates. The differences log MBH/MH are limited by | log MBH/MH| ≤ 0.62, which implies that the two methods of estimating black hole masses by the rapid-variability timescales and the reverberation mapping method should be reliable. We also discuss the origin of the double-peaked Hβ emission line in PKS 1510-089 and show it to be probable that the double-peaked Hβ emission line is mainly produced by a nonaxisymmetric accretion disk surrounding the central Kerr black hole.
    The Astronomical Journal 12/2007; 130(6):2506. DOI:10.1086/497163 · 4.05 Impact Factor
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    ABSTRACT: We have compiled sample of 17 GeV γ-ray–loud blazars, for which rapid optical variability and γ-ray fluxes are well observed, from the literature. We derive estimates of the masses, the minimum Kerr parameters amin, and the size of the emission regions of the supermassive black holes (SMBHs) for the blazars in the sample from their minimum optical variability timescales and γ-ray fluxes. The results show that (1) the masses derived from the optical variability timescale (MH) are significantly correlated with the masses from the γ-ray luminosity (M); (2) the values of amin of the SMBHs with masses MH ≥ 108.3 M (three out of 17 objects) range from ~0.5 to ~1.0, suggesting that these SMBHs are likely to be Kerr black holes. For the SMBHs with MH < 108.3 M, however, amin = 0, suggesting that a nonrotating black hole model cannot be ruled out for these objects. In addition, the values of the size of the emission region, r*, for the two kinds of SMBHs are significantly different. For the SMBHs with amin > 0, the sizes of the emission regions are almost within the horizon (2rG) and marginally bound orbit (4rG), while for those with amin = 0 they are in the range (4.3–66.4)rG, extending beyond the marginally stable orbit (6rG). These results may imply that (1) the rotational state, the radiating regions, and the physical processes in the inner regions for the two kinds of SMBH are significantly different and (2) the emission mechanisms of GeV γ-ray blazars are related to the SMBHs in their centers but are not related to the two different kinds of SMBH.
    The Astronomical Journal 12/2007; 126(5):2108. DOI:10.1086/378597 · 4.05 Impact Factor
  • Z. B. Zhang, G. Z. Xie
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    ABSTRACT: In this paper, we have performed a temporal analysis of single pulses from short (46) and long (51) gamma-ray bursts (GRBs) to investigate possible differences in their properties. In particular we pay detailed attention to the asymmetry of pulses. We find that the asymmetry ratio of short GRB pulses clusters around 0.81 and that these pulses are on average more symmetric than those from long GRBs, which have an average value of 0.47. In addition we note that the pulses in short GRBs display exponential rises and fast decays (ERFD) in comparison the fast rise exponential decays (FRED) pulses of long GRBs. The asymmetry ratio does not depend on the full width at half maximum (FWHM) and does not vary with energy channel. Moreover, there is a general trend for slower pulses to be more asymmetric. Finally, we deduce that the asymmetry could be used to probe the emission mechanisms of GRBs.
    Astrophysics and Space Science 06/2007; 310(1):19-23. DOI:10.1007/s10509-007-9390-2 · 2.40 Impact Factor
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    ABSTRACT: Using a theoretical model describing pulse shapes, we have clarified the relations between the observed pulses and their corresponding timescales, such as the angular spreading time, the dynamic time as well as the cooling time. We find that the angular spreading timescale caused by curvature effect of fireball surface only contributes to the falling part of the observed pulses, while the dynamic one in the co-moving frame of the shell merely contributes to the rising portion of pulses provided the radiative time is negligible. In addition, the pulses resulted from the pure radiative cooling time of relativistic electrons exhibit properties of fast rise and slow decay (a quasi-FRED) profile together with smooth peaks. Besides, we interpret the phenomena of wider pules tending to be more asymmetric to be a consequence of the difference in emission regions. Meanwhile, we find the intrinsic emission time is decided by the ratios of lorentz factors and radii of the shells between short and long bursts. Based on the analysis of asymmetry, our results suggest that the long GRB pulses may occur in the regions with larger radius, while the short bursts could locate at the smaller distance from central engine.
    Astronomische Nachrichten 01/2007; 328(1). DOI:10.1002/asna.200610666 · 1.12 Impact Factor

Publication Stats

667 Citations
276.11 Total Impact Points

Institutions

  • 1995–2010
    • Yunnan University
      • Department of Physics
      Kunming, Yunnan, China
  • 1992–2010
    • Chinese Academy of Sciences
      • Graduate School
      Peping, Beijing, China
  • 1993–1999
    • Yunnan Normal University
      • Department of Physics
      Yün-nan, Yunnan, China
  • 1997–1998
    • Guangzhou Normal University
      Shengcheng, Guangdong, China
  • 1987–1997
    • Academia Sinica
      T’ai-pei, Taipei, Taiwan
  • 1990–1992
    • University of Science and Technology of China
      Luchow, Anhui Sheng, China
  • 1986–1991
    • Government of the People's Republic of China
      Peping, Beijing, China