Infrared variability of the BL lacertae object OJ287 since its outburst in 1983

In early 1983, OJ287 was seen to undergo an outburst in its optical and infrared emission¹. Since then optical monitoring studies ^2-4 have shown a general decline in the source brightness, with considerable fluctuations. We have monitored the near-infrared emission since the outburst. The fluxes have fluctuated considerably, with the lowest recordings being an order of magnitude less than those measured during the outburst. We have found an excellent correlation between infrared flux and spectral index; as the source gets fainter the spectrum gets steeper, and vice versa. We interpret this in terms of outbursts being due to injection or reacceleration of electrons with a constant energy index which subsequently steepens as the electrons are affected by radiation losses.