A flare in the millimetre to IR spectrum of 3C273

Over the past two years some of us (E.I.R., P.A.R.A., W.K.G., M.G.S., and I.G.N.) have been monitoring the millimetre and submillimetre spectrum of 3C273 (ref. 1). We have presented elsewhere a quiescent millimetre-to-far-IR spectrum2 with an index α = −0.7 (Sv α vα) connecting smoothly to the radio and mid-IR. Our discovery of a concurrent flare in the IR-to-near-millimetre spectrum of 3C273 implies that the emission over this range of frequency originates in the same region of the source. The flare was seen to propagate to longer wavelengths whilst decaying at shorter wavelengths. The time scale of the flare is suggestive of an event within the central 0.1 pc of the source. Millimetre wavelength variability of 3C273 has been reported3,4 but with very little temporal overlap with our data. Rieke and Lebofsky16 have reviewed the 2.2 and 10 µm variability