The Wikipedia page on the "Cigar Galaxy" (M82) has the following summary about an "unknown object":
In April 2010, radio astronomers working at the Jodrell Bank Observatory of the University of Manchester in the UK reported an object in M82 that had started sending out radio waves, and whose emission did not look like anything seen anywhere in the universe before.
A subsequent article in New Scientist dated 13 December 2010 offers the following update:
The object is still a puzzle, says co-discoverer Tom Muxlow. “It was still there the last time we looked, so its lifetime is now well over a year,” he says. “We are continuing to monitor this object.”
I can find a number of other references to this unknown object, but nothing more recent than 2010. The articles suggest it could perhaps be a new type of microquasar, since it shares some similarities; however, it doesn't have the high X-ray output that known microquasars exhibit.
Has the mystery been solved, or is this still an area of active research?