Flat-Spectrum Radio Quasars from SDSS DR3 Quasar Catalogue

Abstract

We constructed a sample of 185 Flat Spectrum Radio Quasars (FSRQs) by cross-correlating the Shen et al.'s SDSS DR3 X-ray quasar sample with FIRST and GB6 radio catalogues. From the spectrum energy distribution (SED) constructed using multi-band (radio, UV, optical, Infrared and X-ray) data, we derived the synchrotron peak frequency and peak luminosity. The black hole mass and the broad line region (BLR) luminosity (then the bolometric luminosity) were obtained by measuring the line-width and strength of broad emission lines from SDSS spectra. We define a subsample of 118 FSRQs, of which the nonthermal jet emission is thought to be dominated over the thermal emission from accretion disk and host galaxy. For this subsample, we found 25 FSRQs having synchrotron peak frequency > 10^{15} Hz, which is higher than the typical value for FSRQs. While only a weak anti-correlation is found between the synchrotron peak frequency and peak luminosity, it becomes significant when combining with the Wu et al.'s sample of 170 BL Lac objects. At similar peak frequency, the peak luminosity of FSRQs with $\nupeak > 10^{15}$ Hz is systematically higher than that of BL Lac objects, with some FSRQs out of the range covered by BL Lac objects. Although high $\nupeak$ are found in some FSRQs, they do not reach the extreme value of BL Lacs. For the subsample of 118 FSRQs, we found significant correlations between the peak luminosity and black hole mass, the Eddington ratio, and the BLR luminosity, indicating that the jet physics may be tightly related with the accretion process.