We have a possible size constraint
The object was changing for a period of at least 200 days (approx) so because of the speed of light, it can't be much larger than about half a light year, although it could be a lot smaller. This assumes we saw most of the light curve, and not just a tiny piece of it while it was visible to us. If we did see a long-lived phenomenon that was only bright enough to be seen for a very short period of time, it could be much bigger.
Very strange.