The 1994 outburst

One of the problems was that nobody knew quite what to expect in 1994. There were plenty of predictions as to exactly when the outburst might occur, most in happy disagreement between themselves, but nobody knew which, if any, would be the correct one. The best prediction seemed to suggest that the most probable date was mid-November 1994 with a second outburst about 13 months later, but nobody was sure how much any prediction could be trusted. Figure 1 also suggested that the size of the size of the outbursts seemed to vary with a longer cycle of some 60 years – the outbursts in 1913 and 1972 were especially large and after 1913 they became much smaller again before getting progressively larger while, in 1983 the outburst had been much smaller than in 1972. It looked like 1994 would come near the bottom of the cycle and that the outburst would be quite small and then, after 1994 successive outbursts would get bigger and bigger, with another especially large one due around 2031. If a small outburst really did happen in November 1994 the periodicity would be confirmed.

A major international monitoring effort started in Fall 1993. Initially OJ287 was extremely faint but, as more data came in through, early 1994, something started to appear in the data. OJ287 was brightening slowly, but persistently. Could this be the big outburst that we were awaiting?

As we watched, the brightness of this blazar continued to increase all through 1994 until we lost it behind the Sun on June 13th. It was still fainter than it had been briefly in December, but it was going in the correct direction. What would happen during the nearly 3 months that it would be too close to the Sun in the sky to be observable? Might the outburst happen without us ever seeing it?

On September 8th the amazing Canadian amateur, Paul Boltwood, recovered OJ287 low in the dawn sky in Canada – far too low for any professional telescope to observe. There was some consternation when we realised that it was quite a bit fainter than it had been in June. Over the next three weeks though it was brightening constantly and, by the end of September it was obvious that something interesting was happening. Through October OJ287 continued its steady increase in brightness until, lo and behold, on November 11th 2004 it broke fractionally through magnitude 14 for a few hours before starting to fade rapidly again. What was more, the maximum was the faintest that had ever been seen, with the possible exception of 1924 when the data was very poor.

It seemed that the predictions of the binary black hole model had been amply confirmed. 

OJ287 faded rapidly and by April 1995 was as faint as we had ever seen it. Just before disappearing behind the Sun again though it was brightening again. Thirteen months after its first outburst, on December 16th 1995, OJ287 reached an almost identical magnitude as it had at maximum 13 months earlier. The fact that the second maximum occurred on schedule confirmed the model prediction almost to the letter.
 


 

Figure 2 – The light curve of OJ287 between 1993 and 1995. Two big brightenings are seen that seem to confirm the predictions of the binary black hole model. Image prepared by the author.