Rapid variability of 3C273 at 300 GHz

With a broadband bolometer mounted on the 3.6-m ESO telescope, 3C273 has been measured at 300 GHz six times in six days. During this series of measurements, a sudden drop in flux density by 11.6 + or - 2.9 Jy (spectral index assumed to be zero, and all known errors included) was observed. In an interpretation with the model of bulk relativistic motion,the brightness temperature inferred can be combined with the observed superluminal motion to derive strict limits on the model parameters.