Unusual Central Engine Activity in the Double Burst GRB 110709B
  The double burst, GRB 110709B, triggered Swift/BAT twice at 21:32:39 UT and 21:43:45 UT, respectively, on 9 July 2011. This is the first time we observed a 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. 
Bin-Bin Zhang, David Burrows, Bing Zhang, Peter Meszaros, Xiang-Yu   Wang, Giulia Stratta, Valerio D'Elia, Dmitry Frederiks,...
astro-ph.HE