It might be the space-time disturbance created during the formation of a primordial, supermassive black hole finally arriving here, after propagating since a very small fraction of a second after the big bang.
If the signal is verified as real, and especially if we get another one (I mean, we just turned LIGO on, cosmologically speaking), there will be an all-out race within the cosmological modeling community to reproduce it. If people are successful, and especially if they stay within the bounds of uncertainty surrounding the period of inflation, that's a bingo. Even if the models can generate a wave that looks good at first, they'll have to account for stuff like how much the waveform could be dispersed after propagating across a constantly-inflating universe. Here's an article on primordial black holes and gravity waves, but it does not include mention of the new event, as it may have been published just hours prior. Edit: Well, the article focuses on small primordial black holes, sprinkled around locally, but I was talking about an event right after the big bang that created a black hole that goes on to serve as the core of a galaxy. Yeah, observational cosmology is still kinda like the wild west of physics. What you were supposed to say: NOPE, STILL RAMA, BETCH