Did a gamma ray burst accompany LIGO's gravity wave detection?

Last week's announcement that Gravitational Waves (GW) have been detected for the first time--as a result of the merger of two black holes--is huge news. But now a Gamma Ray Burst (GRB) originating from the same place, and that arrived at Earth 0.4 seconds after the GW, is making news. Isolated black holes aren't supposed to create GRB's; they need to be near a large amount of matter to do that.