Linearly Polarized X-Ray Flares following Short Gamma-Ray Bursts

Soft X-ray flares were detected to follow the short-duration gamma-ray burstGRB 050724. The temporal properties of the flares suggest that they are likelydue to the late time activity of the central engine. We argue that if shortGRBs are generated through compact star mergers, as is supported by the recentobservations, the jet powering the late X-ray flares must be launched viamagnetic processes rather than via neutrino-antineutrino annihilations. As aresult, the X-ray flares following short GRBs are expected to be linearlypolarized. The argument may also apply to the X-ray flares following long GRBs.Future observations with the upcoming X-ray polarimeters will test thisprediction.Comment: 4 pages (no figure), accepted for publication in ApJL, typos correcte