On the masses of black-holes in radio-loud quasars

The central black-hole masses of a sample of radio-loud quasars are estimated by using the data of $H_{\beta}$ line-width and the optical continuum luminosity. The vast majority of the quasars in this sample have black-hole masses larger than $10^{8} M_{\odot}$, while a few quasars may contain relatively smaller black-holes. We found a significant anti-correlation between the radio-loudness and the central black-hole mass. It might imply that the jet formation is governed by the black-hole mass.Comment: 5 pages, two figures are added, accepted by MNRAS Letter

Why are some BL Lacs detected by \fermi, but others not ?

By cross-correlating an archival sample of 170 BL Lacs with 2 year \fermilat AGN sample, we have compiled a sample of 100 BL Lacs with \fermi detection (FBLs), and a sample of 70 non-\fermi BL Lacs (NFBLs). We compared various parameters of FBLs with those of NFBLs, including the redshift, the low frequency radio luminosity at 408 MHz ($L_{\rm 408MHz}$), the absolute magnitude of host galaxies ($M_{\rm host}$), the polarization fraction from NVSS survey ($P_{\rm NVSS}$), the observed arcsecond scale radio core flux at 5 GHz ($F_{\rm core}$) and jet Doppler factor; all the parameters are directly \textbf{measured} or derived from available data from literatures. We found that the Doppler factor is on average larger in FBLs than in NFBLs, and the $Fermi~ \gamma$-ray detection rate is higher in sources with higher Doppler factor. In contrast, there are no significant differences in terms of the intrinsic parameters of redshift, $L_{\rm 408MHz}$, $M_{\rm host}$ and $P_{\rm NVSS}$. FBLs seem to have a higher probability of exhibiting measurable proper motion. These results strongly indicate a higher beaming effect in FBLs compared to NFBLs. The radio core flux is found to be strongly correlated with $\gamma$-ray flux, which remains after excluding the common dependence of the Doppler factor. At the fixed Doppler factor, FBLs have systematically larger radio core flux than NFBLs, implying lower $\gamma$-ray emission in NFBLs since the radio and $\gamma$-ray flux are significantly correlated. Our results indicate that the Doppler factor is an important parameter of $\gamma$-ray detection, the non-detection of $\gamma$-ray emission in NFBLs is likely due to low beaming effect, and/or low intrinsic $\gamma$-ray flux, and the gamma-rays are likely produced co-spatially with the arcsecond-scale radio core radiation and mainly through the SSC process.Comment: 6 pages, 6 figures, accepted by A&

Surface flux transport modeling for solar cycles 15--21: effects of cycle-dependent tilt angles of sunspot groups

We model the surface magnetic field and open flux of the Sun from 1913 to 1986 using a surface flux transport model, which includes the observed cycle-to-cycle variation of sunspot group tilts. The model reproduces the empirically derived time evolution of the solar open magnetic flux, and the reversal times of the polar fields. We find that both the polar field and the axial dipole moment resulting from this model around cycle minimum correlate with the strength of the following cycle.Comment: Accepted for publication by Ap

Helical motions in the jet of blazar 1156+295

The blazar 1156+295 was observed by VLBA and EVN + MERLIN at 5 GHz in June 1996 and February 1997 respectively. The results show that the jet of the source has structural oscillations on the milliarcsecond scale and turns through a large angle to the direction of the arcsecond-scale extension. A helical jet model can explain most of the observed properties of the radio structure in 1156+295.Comment: 6 pages, 2 figures, to appear in New Astronomy Reviews (EVN/JIVE Symposium No. 4, special issue