Compact symmetric objects as radio flux density calibrators

We present results from the first intensive monitoring campaign of a sample of compact symmetric objects (CSOs). We observed seven CSOs at 8.5 GHz ove r a period of eight months, with an average spacing between observations of 2.7 days. Our results show that, as predicted, the flux densities of the C SOs are extremely stable; the mean rms variability of the sample was 0.7% i n flux density. The low variability of the CSOs makes them excellent flux d ensity calibrators at this frequency. We recommend that at least four CSOs be included in any VLA monitoring campaign that requires precise epoch-to-e poch calibration, such as those to measure gravitational lens time delays. The CSO data enable the correction of small systematic errors in the primar y flux calibration.