In 1999 , the highly compact and variable BL Lac object AO 0235+164 was identified as the highest brightness temperature active galactic nucleus observed with the VLBI Space Observatory Programme ( VSOP ) , with T _ { B } > 5.8 \times 10 ^ { 13 } K \citep fre00 .
The sub-milliarcsecond radio structure of this source has been studied with dual-frequency ( 1.6 and 5 GHz ) , polarization-sensitive VSOP observations during 2001 and 2002 .
Here we present the results of this monitoring campaign .
At the time of these observations , the source was weakly polarized and characterized by a radio core that is clearly resolved on space–ground baselines .