Unusual Central Engine Activity in the Double Burst GRB 110709B

The double burst, GRB 110709B, triggered the Swift/Burst Alert Telescope (BAT) twice at 21 32 39 UT and 21 43 45 UT, respectively, on 2011 July 9. This is the first time we observed a gamma-ray burst (GRB) with two BAT triggers. In this paper, we present simultaneous Swift and Konus-WIND observations of this unusual GRB and its afterglow. If the two events originated from the same physical progenitor, their different time-dependent spectral evolution suggests they must belong to different episodes of the central engine, which may be a magnetar-to-BH accretion system.