Compact Symmetric Objects as Radio Flux Density Calibrators

We present results from the first intensive monitoring campaign of a sampleof Compact Symmetric Objects (CSOs). We observed seven CSOs at 8.5 GHz over aperiod of eight months, with an average spacing between observations of 2.7days. Our results show that, as predicted, the flux densities of the CSOs areextremely stable; the mean RMS variability of the sample was 0.7% in fluxdensity. The low variability of the CSOs makes them excellent flux densitycalibrators at this frequency. We recommend that at least four CSOs be includedin any VLA monitoring campaign which requires precise epoch-to-epochcalibration, such as those to measure gravitational lens time delays. The CSOdata enable the correction of small systematic errors in the primary fluxcalibration.Comment: To appear in the Astronomical Journal. 19 pages, 5 figure