Rapid infrared and optical variability in the bright quasar 3C273
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The magnitude and timescale of variations in the luminosity of quasars provide crucial constraints on the mechanism of emission and the physical size of the emitting region. We have observed variations by a factor of two in the infrared flux from the bright quasar 3C273 on a timescale as short as one day. Variations of this magnitude, over such short periods, are unprecedented. In February 1988, the behaviour of the source changed from having a stable infrared flux and slow optical variations (on timescales of weeks or months) to a state characterized by recurrent infrared and optical flaring. The optical variations were of several per cent per day, changing from increase to decrease approximately every week. The amplitude of the repeated optical flares was 30-40%. The data are consistent with re-injection/acceleration of electrons followed by rapid cooling. The inferred magnetic field is 0.7 gauss and the data are marginally consistent with no relativistic beaming. 1988 Nature Publishing Group.