What is the difference between an ultra-long GRB and a long GRB?

The new class of ultra-long gamma-ray bursts is a fascinating class of events, where the very long duration of these events theoretically allows for pointing sensitive instruments during the prompt phase. However, this is complicated by the initially uncertain nature of the event. How to predict that an event will be an ultralong GRB, i.e. duration more than 3 hours, while high-energy detectors are recording only the first tens of seconds? We present here our study about potential discriminators that can distinguish ultra-long GRBs from normal long ones during the first minute of the prompt event. This would allow for the observation of the source with a large set of detectors at various energies.