H. Z. Li

PERIODICITY ANALYSIS OF THE RADIO CURVE OF PKS 1510-089 AND IMPLICATIONS FOR ITS CENTRAL STRUCTURE

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 Metsahovi Radio Observatory, and find evidence of quasi-periodic outbursts. The light curves show great activity with very complicated non-sinusoidal variations. Using Jurkervichs 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) approximate to 2p(1). In addition, these results are in good agreement with the periodic deep flux minima of 1.84 +/- 0.1 yr ( half period similar to 0.92 +/- 0.03 yr) observed by us and other authors in the optical band in 2002, 2004, and 2005.

Correlation between eddington ratios and broad-line luminosities in flat-spectrum radio quasars, BL lacertae objects, and radio galaxies

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 two-color diagram: The "double-hump'' behavior at the radio band and the evolution of blazars

We compiled a sample of 29 flat-spectrum radio quasars (FSRQs) and 48 BL Lac objects for which both B - V and U - B are available. The two-color (U - B, B - V) stellar evolution diagram of FSRQs and BL Lac objects in this sample shows that FSRQs and BL Lac objects can be considered to be in the same family, but they occupy different extreme regions in the diagram. The result of the two- color diagram of FSRQs and BL Lac objects in this paper is consistent with the intrinsic accretion rate - luminosity relation for FSRQs and BL Lac objects that was obtained in a previous paper. In addition, based on the quasi-simultaneous spectral properties of core-dominated radio sources observed by Punsly, we compiled another sample of FSRQs and BL Lac objects for which the quantities Delta log [(F-nu)(cm)/(F-nu)(mm)] have been well obtained. We found that there is a significant correlation between the intrinsic bolometric luminosity log L-bol(in) and the quantity Delta. We also found that FSRQs have a relatively higher bolometric luminosity and larger Delta than BL Lac objects. This result is also consistent with the intrinsic accretion rate - luminosity relation because the physical parameters Delta are strongly correlated with the accretion rates (M) and nuclear gas densities.

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.

The Periodicity Analysis of the Light Curve of 3C 279 and Implications for the Precession Jet

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 Pobs and the precession period Pp given by Rieger and our result, the precession period of jet in 3C 279 is P(p) similar or equal to 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.

Multiband Variability Analysis of 3C 454.3 and Implications for the Center Structure

We have analyzed the light curves of 3C 454.3 at the infrared, optical, soft X-ray (0.3-10 keV), and γ-ray (0.1-300 GeV) waveband, and found the evidence of quasi-periodicity. The light curves show that 3C 454.3 is a strongly active object. A period signal of P = 210.8 ± 12.1 days is confirmed by two methods consistently: the Lomb-Scargle periodogram and the Jurkevich method. The variations of the infrared, optical, soft X-ray, and γ-ray are well correlated, which suggests that these seven band emissions originate from the same population of electrons in the jet. The multifrequency variations in the emission fluxes of 3C 454.3 may be caused by the nonballistic helical motion of emitting components in the jet, which has the precession and the helical magnetic field. Moreover, these provide some evidence for the existence of a supermassive binary black hole (SMBBH) system in the center of 3C 454.3.

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.

Multiband Variability Analysis of Mrk 421

We have assembled the historical variability data of Mrk 421 at radio 15 GHz, X-ray and gamma-ray bands, spanning about 6.3, 10.3 and 7.5 yr, respective- ly. We analyzed the variability by using three methods. The results indicated that there is a period of 287.6 +- 4.4 days for 15 GHz, 309.5 +- 5.8 days for X- ray and 283.4+- 4.7 days for gamma-ray, respectively. This period can be reasonably explained by the nonballistic helical motion of the emitting material. The cor- relation analysis suggested that the variabilities of radio 15 GHz, X-ray and 0-ray are remarkable correlated, and the emission of radio 15 GHz lags behind that of X-ray, and the X-ray flux lags behind the gamma-ray. This suggests that the gamma-ray derives from inverse Compton (IC) scattering of the synchrotron photons, supporting the synchrotron self-Compton (SSC) model. Moreover, the time delay between different wavebands could be explained by the shock-in-jet models, in which a moving emission region produces the radio to gamma-ray activity, implying that the emission region of gamma-ray is closer to the center than ones of X-ray and radio emission.

The broadband spectral energy distributions of SDSS blazars

We compiled the radio, optical and X-ray data of blazars from the Sloan Digital Sky Survey database, and presented the distribution of luminosities and broad-band spectral indices. The distribution of luminosities shows that the averaged luminosity of flat spectrum radio quasars (FSRQs) is larger than that of BL Lacertae (BL Lac) objects. On the other hand, the broadband spectral energy distribution reveals that FSRQs and low energy peaked BL Lac objects have similar spectral properties, but high energy peaked BL Lac objects have a distinct spectral property. This may be due to the fact that different subclasses of blazars have different intrinsic environments and are at different cooling levels. Even so, a unified scheme is also revealed from the color-color diagram, which hints that there are similar physical processes operating in all objects under a range of intrinsic physical conditions or beaming parameters.