Exploring the Connection Between Ultraviolet/optical Variations and Radio Emission in Radio-Quiet Quasars: Clues about the Origin of Radio Emission

The radio emission in radio-quiet quasars (RQQs) has been a long mystery and its physical origin remains unclear. In a previous work we find UV/optical more variable quasars have stronger X-ray emission, indicating a link between disc turbulence and X-ray corona heating. In this work, for the first time, we investigate the relation between UV/optical variability and the radio emission in RQQs selected from SDSS stripe 82 and FIRST radio survey. We median stack the FIRST images and detect clear signals from RQQs in the co-added images of individually radio non-detected sources. Controlling the effects of other parameters, including redshift, black hole mass, bolometric luminosity and Eddington ratio, we find more variable RQQs, which are known to be X-ray relatively brighter, show tentatively weaker radio emission, contrary to the linear X-ray/radio correlation if the radio emission is from or driven by the corona. The discovery also suggests that if the radio emission in RQQs is driven by AGN activity (such as weak jet), the underlying driving process is independent to the disc turbulence which drives UV/optical variability and probably also corona heating. Alternatively, the radio emission could be due to star formation in the host galaxies.