The infrared-millimetre-centimetre flaring behaviour of the quasar 3C 273

Results are presented of an investigation of the IR-cm light curve of 3C 273 for the period 1987-1991, during which several flares were observed. The apparent details of individual flares are shown to be critically dependent on the temporal sampling. Excellent correlation is found between all these wavelengths, but there is a delay between flare onset as sampled in the IR and the emission at longer wavelengths, with a significant difference occurring between 2.0 and 3.3 mm. The emission between IR and 2.0-mm wavelengths is commensurate with a single synchrotron component which is associated with the innermost part of the relativistic jet or the injection region, while the 3.3-13.5-mm wavelength emission probably reflects the evolution of the flaring electron population in the jet and is bound up with optical depth effects. The light curve in shown to be strongly dependent on wavelength, particularly between 3.3 and 8.1 mm for the 1990/1991 events.