Three-Peak GRBs and Their Implications for Central Engines
  GRB 110709B presented a peculiar three-peak lightcurve; this burst twice
triggered the BAT detector onboard Swift. The two triggers were separated by
$\sim 10$ minutes. In order to explain such an event, we unify into a single
description the millisecond (ms) protomagnetar and the collapsar central-engine
models. We find that such a scenario could produce GRBs with three peaks. One
for the ms-protomagnetar stage, a second one for the BH-formation event and a
third one for the collapsar phase. We show that the three peaks for GRB 110709B
originate from different phases of the same collapsing object. We estimate the
energies and timescales of the different episodes of this burst using our model
and compare with previous results as well as with a reanalysis we perform on
the data. We show that not only the light curve, but also the photon index
evolution and the delay between the prompt emission and the afterglow of the
second central-engine activity phase point towards a model like the one
proposed here. We find that, with reasonable assumptions, our model correctly
describes the activity in GRB 110709B. We further suggest careful study of
future GRBs lightcurves which may help show the validity of our model. If our
model is correct, this would be the first time that the formation of a BH from
a core-collapse event is observed unimpededly.
