We present VLBI ( EVN+MERLIN ) observations of a sample of three low-redshift radio-intermediate PG quasars ( RIQ ) with flat and variable radio spectrum ( III Zw 2 , PG 1309+355 , PG 2209+184 ) .
Their radio-to-optical flux ratio ( R ) is slightly lower than the average R for steep-spectrum quasars , but their radio spectral properties are those of core-dominated quasars .
It was proposed previously that these sources might be relativistically boosted jets in radio-weak quasars .
Our VLBI observations now indeed confirm the presence of a high brightness temperature core in all three of these objects — two of them have lower limits on T _ { B } well in excess of 10 ^ { 10 } Kelvin .
Moreover , we find no “ missing-flux ” which means that basically all the flux of these quasars is concentrated in the compact radio core .
As the total radio flux is already at the low end for radio-loud quasars , we can place a strong limit on the presence of any extended emission .
This limit is consistent with the extended emission in radio-weak quasars , but excludes that the flat-spectrum RIQ reside in typical radio-loud quasars .
The observations therefore strongly support the idea that relativistic jets are present in radio-weak quasars and hence that radio-loud and radio-weak quasars have very similar central engines .