Guoxi Xie

Historic light curve and long-term optical variation of BL Lacertae 2200+420

In this paper, historical optical (UBVRI) data and newly observed data from the Yunnan Observatory of China (over similar to 100 yr) are presented for BL Lacertae. Large variations of Delta U = 5.12 mag, Delta B = 5.31 mag, Delta V = 4.73 mag, Delta R = 2.59 mag, and Delta I = 2.54 mag, and color indices of U-B = -0.11 +/- 0.20, B-V = 1.0 +/- 0.11, V - R = 0.73 +/- 0.19, V - I = 1.42 +/- 0.25, R - I = 0.82 +/- 0.11, and B - I = 2.44 +/- 0.29 have been obtained from the literature. The Jurkevich method is used to investigate the existence of periods in the B-band light curve, and a long-term period of 14 yr is found. The 0.6 and 0.88 yr periods reported by Webb et al. are confirmed. In addition, a close relation between B - I and B is found, suggesting that the spectrum flattens when the source brightens.

Search for short variability timescale of the GeV gamma-ray-loud blazars

In this paper we report a brief description of 13 gamma -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 gamma -ray variability and found that during 1995-1996 the TeV gamma -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 CENTRAL BLACK HOLE MASSES AND DOPPLER FACTORS OF THE GAMMA -RAY LOUD BLAZARS

In this paper, the central black hole masses and the Doppler factors are derived for PKS 0528 + 134, PKS 0537-441, 3C 279, PKS 1406 - 074, PKS 1622 - 297, Q1633 + 382, Mkn 501, and BL Lacertae. The masses obtained are in the range of (1-7) 10(7) M-. and compared with that obtained with the Klein-Nishina cross section considered (Dermer & Gehrels 1995). If we considered only the Thomson cross section, the masses are in the range of 2.6 10(6) M-. - 2 10(11) M-. The masses obtained from our method are less sensitive to the flux than those obtained from Dermer & Gehrels (1995) method. The masses obtained from two flares (1991 and 1996 flares) of 3C 279 are almost the same. For 3C 279 and BL Lacertae, viewing angle, theta, and Lorentz factor, Gamma, are estimated from the derived Doppler factor and the measured superluminal velocity. For 3C 279, theta = 10 degrees.9 -15 degrees.6, Gamma = 2.4 - 14.4 for delta = 3.37; theta=8 degrees.45 - 9 degrees.7, Gamma = 2.95 - 11.20 for delta = 4.89; for BL Lacertae, theta = 25 degrees - 29 degrees.4, Gamma = 2.0 - 4.0.

THE MASS-LUMINOSITY RELATION, ACCRETION RATE-LUMINOSITY RELATION, AND EVOLUTIONARY SEQUENCE OF BLAZARS

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 10(7.2) to 10(9.4) M-circle dot, 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 (L-in/L-circle dot)=1.225 log (M/M-circle dot) + 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.

Rapid Optical Variability of Gamma-Ray-loud Blazars

We present the optical (B, V, and R) photometry for nine GeV and/or TeV gamma -ray blazars, which were observed from 2000 through 2001 with the 1 m telescope at Yunnan Astronomical Observatory. The GeV gamma -ray-loud source PKS 1510-089 was very active during our observation period, showing an apparent variation of 2.0 mag within 41 minutes in the R band. This is the most violently rapid variability in our optical monitoring program since 1982. Some physics parameters are calculated for this source, namely, the emission size, Doppler factor delta, the efficiency (eta) for conversion of accreted matter into energy, and luminosity. An eta = 62.2 was obtained, strongly implying that relativistic beaming is responsible for the rapid variability of the gamma -ray-loud source. The influence of variable seeing conditions on the observations was investigated. There is a weak correlation between the observed variability and the local seeing conditions for the object 1ES 2344+51.4.

The Connections between Accretion, Jets, and Blazar Unification

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 ( L-BLR) with the radio core luminosity ( L-R(C)) and the extended radio luminosity ( P-E). A strong correlation between log L-BLR and log L-R(C) 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 L-BLR and log L-R(C) is stronger with the effect of the redshift excluded, and the linear correlation coefficient between log L-BLR and log P-E is also significant. The results seem to show that the coupling of the jet and accretion disk is very tight, so that L-BLR also correlates significantly with extended radio luminosity.

Revisiting the characteristics of the spectral lags in short gamma-ray bursts

In this paper, we restudy the spectral lag features of short bright gamma-ray bursts (T-90 < 2.6 s) with a BATSE time-tagged event sample including 65 single pulse bursts. The cross-correlation technique is adopted to measure the lags between two different energy channels. Meanwhile, we also make an investigation of the characteristics of the ratios between the spectral lag and the full width at half-maximum of the pulses, called relative spectral lags. We conclude that spectral lags of short gamma-ray bursts (SGRBs) are normally distributed and concentrated around the value of 0.014, with 40 per cent of them having negative lags. With Kolmogorov-Smirnov tests, we find that the lag distribution is identical to a normal one caused by white noises, which indicates that the lags of the vast majority of SGRBs are so small that they are negligible or non-measurable, as Norris & Bonnell have suggested.

Spectrophotometry and Photometry for Five Blazars and Their Central Black Hole Masses

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 angstrom, we derived the central black hole masses, M-BH. We also estimated the relevant black hole masses, M-H, using rapid-variability timescales and our new formula for black hole mass estimates. The differences log M-BH/M-H are limited by vertical bar log M-BH/M(H)vertical bar <= 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 H beta emission line in PKS 1510-089 and show it to be probable that the double-peaked H beta emission line is mainly produced by a nonaxisymmetric accretion disk surrounding the central Kerr black hole.

The infrared and optical variability of OJ 287

In this paper, the long-term historical optical (UBVRI) and near-infrared (JHK) data are presented with some new observations in the optical (February 1994-January 1995) and near-infrared (November 1995) bands included for BL Lac object OJ 287. The new optical data in V-band are in agreement with the results reported by other authors (Sillanpaa et al. 1996a; Arimoto et al. 1997), a close correlation between the color index of B - V and the magnitude V has been obtained from our new observations. The new infrared observations presented here indicate that the source was at a high level in the infrared band during the observation period. From the available literature, we have got that the largest variations for UBVRIJHK bands are respectively: Delta U = 4.(m)72; Delta B = 5.(m)93; Delta V = 5.(m)18; Delta R = 4.(m)45; Delta I = 4.(m)07; Delta J = 3.(m)87; Delta H = 3.(m)78; Delta K = 3.(m)54. A strong correlation is found between the optical and near-infrared bands when the DCF method is used, which suggests that these two bands have the same emission mechanism.

Susceptibility-based positive contrast MRI of brachytherapy seeds.

To provide visualization of the brachytherapy seeds and differentiation with natural structures in MRI by taking advantage of their high magnetic susceptibility to generate positive‐contrast images.