It's more likely Napoleon rising from the grave than the IRA..
According to the reddit live thread the police said they have found a 2nd device and are performing a controlled explosion on it, but no confirmation on that one as far as im aware.
2nd suspected device near arena that the police will do a controlled explosion.
https://twitter.com/gmpolice/status/866813662505447424
2nd device, Police are performing a controlled explosion.