Evidence for a population of beamed radio-intermediate quasars

Whether radio-intermediate quasars possess relativistic jets as radio-loud quasars do is an important issue in the understanding of the origin of radio emission in quasars. In this paper, using the two-epoch radio data obtained during the Faint Images of the Radio Sky at Twenty cm( FIRST) and NRAOVLA Sky Survey ( NVSS), we identified 89 radio-variable sources in the Sloan Digital Sky Survey ( SDSS). Among them, more than half are radio-intermediate quasars ( RL = f(20) cm/f(2500) (angstrom) < 250). For all objects with available multiple-band radio observations, the radio spectra are either flat or inverted. The brightness temperature inferred from the variability is larger than the synchrotron self-Compton limit for a stationary source in 87 objects, indicating relativistic beaming. Considering the sample selection and the viewing angle effect, we conclude that relativistic jets probably exist in a substantial fraction of radio-intermediate quasars.