Variability of the BL Lacertae object AO0235+164


WE can summarise previous1–3 discussion of the problem of excessive Compton scattering in variable compact non-thermal sources by saying that the small size implied by rapid variability leads to too large a probability that a given electron will Compton-scatter one of the emitted photons, leading to an excessive X-ray flux. The basic assumptions underlying these difficulties are that the time-variable radiation is produced by the incoherent synchrotron process by electrons with large pitch angles in randomly oriented magnetic fields, and that the objects are at the cosmological distances implied by their redshifts. We present here a crude model of the recently observed outburst4 of AO0235+164 in the near infrared and visible, where variability of up to 30% on time scales of 1 or 2 d has been noted. In our model the assumptions of large pitch angle and randomly oriented fields are relaxed5 and the model accords with our previous discussion3 of the low-frequency variability of the radio sources 3C454.3 and CTA 102.

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COCKE, W., PACHOLCZYK, A. Variability of the BL Lacertae object AO0235+164. Nature 265, 608–609 (1977).

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