Jiang-Shui Zhang

Long-term variation time scales in OJ 287

The light curve data from 1894 to 2008 are compiled for the BL Lacertae object OJ 287 from the available literature. Periodicity analysis methods (the Discrete Correlation Function-DCF, the Jurkevich method, the power spectral (Fourier) analysis, and the CLEANest method) are performed to search for possible periodicites in the light curve of OJ 287. Significance levels are given for the possible periods. The analysis results confirm the existence of the 12.2 ± 0.6 yr time scale and show a hint of a ~53 yr time scale. The 12.2±0.6 yr period is used as the orbital period to investigate the supermassive binary black hole system parameters.

Brightness temperature for 166 radio sources

Using the database of the University of Michigan Radio Astronomy Observatory (UMRAO) at three radio frequencies (4.8, 8 and 14.5 GHz), we determined the short-term variability timescales for 166 radio sources. The timescales are 0.15 d (2007+777) to 176.17 d (0528–250) with an average timescale of Δ t obs = 17 . 1  16 . 5 d for the whole sample. The timescales are used to calculate the brightness temperatures, T B . The value of log T B is in the range of log T B = 10.47 to 19.06 K. In addition, we also estimated the boosting factor for the sources. The correlation between the polarization and the Doppler factor is also discussed.

The estimations of four basic parameters for gamma-ray loud blazars

The method used in our previous papers is adopted to estimate four basic parameters (the central black hole mass ( M ), the boosting factor (or Doppler factor) ( δ ), the propagation angle ( Φ ) and the distance along the axis to the site of the γ -ray production ( d )) for 59 γ -ray loud blazars (20 BL Lacertae objects and 39 fl at spectrum radio quasars). The central black hole masses estimated for this sample are in a range of from 10 7 M ⊙ to 10 9 M ⊙ In the case of black hole mass, there is no clear difference between BL Lacertae objects and fl at spectrum radio quasars, which is consistent with the previous results suggesting that the central black hole masses do not play an important role in the evolutionary sequence of blazars

Extragalactic H2O Megamaser Sources： Central Black Holes, Nuclear X-ray and Maser Emissions

Extragalactic H2O megamasers are typically found within the innermost few parsecs of active galaxy nuclei (AGN) and the maser emission is considered to be excited most likely by the X-ray irradiation of the AGN. We investigate a comprehensive sample of extragalactic H2O masers in a sample of 38 maser host AGN to check potential correlations of the megamaser emission with parameters of the AGN, such as X-ray luminosity and black hole (BH) masses. We find a relation between the maser luminosities and BH masses, LH2O∝MBH3.6±0.4, which supports basically the theoretical prediction. The relation between the maser emission and X-ray emission is also confirmed.

XMM-Newton observations of H2O maser galaxy NGC 7479

The XMM-Newton observations of H 2 O megamaser galaxy NGC 7479 are presented. Its smoothed X-ray image clearly shows spiral morphology, which matches well with its optical asymmetric spiral structure. One prominent source can be found at the tip of its northern spiral arm, which is much brighter than its nuclear X-ray source (about a 50% higher count rate). For the nuclear source (a circular region with a radius of 20 ), the spectra show soft excess below 2 keV and a strong iron Kα emission line. The best fitting model includes a partially absorbed model for the hard continuum and one thermal plasma model for the soft scatter component. Both the high column density ( N H ∼ 6.88 × 10 23 cm -2 ) and strong fluorescent iron line (with an equivalent width of ∼1.5 keV) support the existence of one heavily obscured AGN. For the bright prominent source, its radial profile is consistent with that of a single point-like source. Its spectra are extracted from the circular region around its peak, with a radius of 20´´ and 6´´ respectively and both spectra show no significant difference. Four alternative models for the ultra-luminous X-ray source (ULXs) can reproduce the spectra well: an absorbed power law, thermal bremsstrahlung, multicolor blackbody disk plus another blackbody or power law. Further observations (e.g., the tremendous improvement in the spatial resolution of the Chandra X-ray observations) and studies are desirable for probing the nature of this prominent source. In addition, we also estimate the mass of its central engine to be 1.18×10 7 M ⊙ and maser disk parameters: the disk radius of ∼0.7 pc and the dimensionless accretion rate ( L 2-10keV / L Edd ) of 1.2×10 -4 .

ON THE X-RAY PROPERTIES OF H2O MASER HOST GALAXIES

All galaxies beyond the Magellanic clouds with detected H2O maser emission so far are investigated and their X-ray observations are collected in detail to probe the X-ray properties of this special kind of galaxies. The soft excess and the strong iron emission line are commonly presented in their X-ray spectrum. Similar to the spectra of normal Seyfert 2 galaxies, the X-ray soft components are usually explained well by two alternative models or their combination: the absorbed power law model and the thermal emission model. The hard X-ray continua are usually flat, which should be caused by the increase of the reflection component, with the increase of the absorbing material density. Modeling their X-ray spectra shows that high absorbing column density is prevalent in our H2O megamaser host AGNs. Further, we investigate a possible relation between the iron line emission and the nuclear X-ray emission. It shows no significant correlation between the equivalent width (EW) of the neutral FeKα emission line (~ 6.4 keV) and the intrinsic nuclear X-ray luminosity. However, one trend appears clearly — the EW of the iron line decreases with the increase of the observed X-ray luminosity for our H2O maser galaxies. We also estimate the accretion rate of H2O maser host AGNs and the results show that maser galaxies may have a higher accretion rate than nonmaser Seyfert galaxies. In addition, possible relations between the EW of the iron line with the accretion rate and the central black hole mass are investigated and no significant trend of correlation can be found between them.

Spectral Indices of Core and Extended Components of Extragalactic Radio Sources

We use observed peak and total flux densities at 6cm and 20cm to determine the spectral indices separately for the core and extended components of QSOs and galaxies, as well as their core-dominance parameters. Our results indicate that 1) Nine QSOs show both greater than 1.0 core-dominance parameters (those objects should be blazars) and greater than 0.5 spectral indices. The average core spectral index is Core = 0.85±0.21 for the nine blazars, which implies that it is not reliable to use radio = 0.0 for blazars. For the dierent subclasses, the core and extended spectral indices are as follows: for the blazars, Core = 0.22±0.06 and Ext =0.77±0.12; the galaxies, Core = 1.01±0.13 and Ext =0.83±0.21, and for

Oxygen isotopic ratios toward molecular clouds in the Galactic disk

We present our observations of the J = 1 − 0 rotation transitions in molecular isotopes C 18 O and C 17 O toward a sample of molecular clouds with different galactocentric distances, using the Delingha 13.7 m (DLH 13.7 m) telescope, administered by Purple Mountain Observatory, and its 9-beam SIS receiver. Complementary observations toward several sources with large galactocentric distance are obtained with the IRAM 30m and Mopra 22m telescopes. C 18 O/C 17 O abundance ratios reflecting the 18 O/ 17 O isotope ratios are obtained from integrated intensity ratios of C 18 O and C 17 O. We derived the ratio value for 13 sources covering a galactocentric distance range of 3 kpc to 16 kpc. In combination with our mapping results that provide a ratio value of 3.01±0.14 in the Galactic center region, it shows that the abundance ratio tends to increase with galactocentric distance, i.e., it supports a radial gradient along the Galactic disk for the abundance ratio. This is consistent with the inside-out formation scenario of our Galaxy. However, our results may suffer from small samples with large galactocentric distance. Combining our data with multitransition lines of C 18 O and C 17 O will be helpful for constraining opacities and abundances and further confirming the Galactic radial gradient shown by the isotope ratio 18 O/ 17 O.

Oxygen isotope ratio studies in the Galactic center region

Sgr C ~ -56 km/s 3.53±0.09 Gas kinematics of the Galactic center region (GC) show that gas in the halo flow inside toward the disk and gas in the outskirts of the disk fall further toward the GC (e.g., Fukui et al. 2006; Binney et al. 1991; Rodriguez-Fernandez &Combes 2008). Isotope ratios are considered to be good tool to discriminate between gas flowing towards the disk and gas already residing in the disk of central galactic plane (Riquelme et al. 2010). Systematic study on the ratio of 18O to 17O of the Galaxy, by C18O and C17O (similar chemical and excitation properties and both tend to be optically thin ): 1) Detailed mapping of GC different molecular clouds: in disk, halo, X1-X2 orbits à check different properties of gas in the halo and disk and understand GC kinematics. 2) Combining with observations in different galactocentric distance clouds, to check the existence of 18O/17O gradient at large scale. Preliminary results of molecular clouds in Galactic center region are presented: Sgr A, Sgr B2, Sgr C, Sgr D, 1.◦3 complex in the disk of CMZ, and M+5.3-0.3 in halo. Ø Integrated intensity ratio of C18O/C17O (frequency corrected) à isotopic ratio 18O/17O • Optical thin; Fractionation? Selective photo-dissociation?

SUPERMASSIVE BLACK HOLE MASSES FOR BLAZARS

In this work, we determine the central black hole mass for a sample of blazars including 30 γ-ray loud blazars with available variability timescales. The γ-ray energy, the emission size and the property of a two-temperature accretion disk are used to determine the absorption depth. If we take the intrinsic γ-ray luminosity to be λ times the Eddington luminosity, i.e. , then we have following results: the masses of the black hole are in the range of 0.59 ~ 67.99 × 107M⊙(λ = 1.0) or 0.90 ~ 104.13 × 107M⊙(λ = 0.1). Blazars are also discussed.