THE INFRARED MILLIMETER CENTIMETER FLARING BEHAVIOR OF THE QUASAR 3C 273

The infrared-centimetre fight curve of 3C 273 is investigated for the period 1987-91, during which time 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 it is clear that 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 is shown to be strongly dependent on wavelength, particularly between 3.3 and 8.1 mm for the 1990/91 events. The quiescent infrared flux is dominated by a stable component which may well be due to dust. We note a variation in the quiescent infrared spectral slope which is strongly correlated with J-band flux and can be interpreted as a flickering in the underlying synchrotron spectrum.