Shu-Bai Zhou

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.

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.

Estimates of AGN Black Hole Mass and Minimum Variability Timescale

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 (M,) 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 M-s, M-k and M-d, respectively. We compared each of them with M-sigma individually and found that: (1) using the minimum variability timescale with the Kerr black hole theory leads to small differences between M-sigma and M-k, 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 M-sigma and M-s, 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 M-sigma and M-d, 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.

Masses, dimensionless Kerr parameters, and emission regions in GeV gamma-ray-loud blazars

We have compiled sample of 17 GeV gamma-ray-loud blazars, for which rapid optical variability and gamma-ray fluxes are well observed, from the literature. We derive estimates of the masses, the minimum Kerr parameters a(min), 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 gamma-ray fluxes. The results show that (1) the masses derived from the optical variability timescale (M(H)) are significantly correlated with the masses from the gamma-ray luminosity (M(H)(KN)); (2) the values of a(min) of the SMBHs with masses M(H)greater than or equal to10(8.3) M(circle dot)(three out of 17 objects) range from similar to0.5 to similar to1.0, suggesting that these SMBHs are likely to be Kerr black holes. For the SMBHs with M(H) 0, the sizes of the emission regions are almost within the horizon (2r(G)) and marginally bound orbit (4r(G)), while for those with a(min)=0 they are in the range (4.3-66.4)r(G), extending beyond the marginally stable orbit (6r(G)). 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 gamma-ray blazars are related to the SMBHs in their centers but are not related to the two different kinds of SMBH.

A periodicity analysis of the light curve of 3C 454.3

We analyzed the radio light curves of 3C 454.3 at frequencies 22 and 37 GHz taken from the database of Metsahovi Radio Observatory, and found evidence of quasi-periodic activity. The light curves show great activity with very complicated non-sinusoidal variations. Two possible periods, a very weak one of 1.57 +/- 0.12 yr and a very strong one of 6.15 +/- 0.50 yr were consistently identified by two methods, the Jurkevich method and power spectrum estimation. The period of 6.15 +/- 0.50 yr is consistent with results previously reported by Ciaramella et al. and Webb et al. Applying the binary black hole model to the central structure we found black hole masses of 1.53 x 10(9) M-. and 1.86 x 10(8) M-., and predicted that the next radio outburst is to take place in 2006 March and April.

Properties of Low Radio Luminosity RGB BL Lac Objects

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 (alpha(rx)) and each of the luminosities (L-r, L-o, L-x), as well as the relation between the X-ray spectral index ( alpha x) and the radio luminosity ( Lr) for this sample. Our analysis results indicate that (1) plots of (alpha(rx), L-i) ( i denotes r, o, or x) all exhibit the continuity of alpha(rx); ( 2) of 71 low-L-r RGB BL Lac objects (L-5 GHz < 10(25) W Hz(-1)), 24% have alpha(rx) steeper than 0.75, while 79% are distributed in the region 0: 6 < alpha(rx) < 0: 9 and have such a broad scatter in alpha(rx) that alpha(rx) can range from 0.55 to 0.8 for any given value of Lr; ( 3) of 60 low-Lr RGB BL Lac objects ( with alpha(x) available), 20% have alpha(x) flatter than 1, and no correlation is present for alpha(x) versus alpha(x). In addition, no correlation is found between L-o and alpha(rx) 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 L-x versus alpha(rx), which agrees with that reported by Mei et al., and ( 2) more importantly, alpha(rx) 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.

Effects of redshift on the classifying criteria of BL lacertae objects

We have collected a sample of 70 BL Lacs (33 radio-selected BL Lacs and 37 X-ray selected BL Lacs) with multi-waveband data for investigating the classifying criteria of BL Lacertae Objects. For each source, we estimate its luminosities in radio, optical and X-ray, the broad-band spectral index from radio to X-ray and the peak frequency of the synchrotron emission, and make a statistical analysis of the data obtained. Our main results are as follows: (1) The broad-band spectral index and the peak frequency have no correlation with the redshift, while they are inversely correlated with each other and they could be regarded as equivalent classifying criteria of BL Lac objects. (2) There are significant effects of the luminosity/redshift relation on the observed luminosity distribution in our sample, hence, if the radio luminosity is to be used as a classifying criterion of BL Lac objects, it should not be regarded as equivalent to the broad-band spectral index or the peak frequency. (3) Our results supply a specific piece of evidence for the suggestion that the use of luminosities always introduces a redshift bias to the data and show that the location of the peak frequency is not always linked to the luminosity of any wave band.