Linearly polarized X-ray flares following short gamma-ray bursts

Soft X-ray flares were detected following the short-duration gamma-ray burst GRB 050724. The temporal properties of the flares suggest that they are likely due to the late-time activity of the central engine. We argue that if short GRBs are generated through compact star mergers, as is supported by the recent observations, the jet powering the late X-ray flares must be launched via magnetic processes rather than via neutrino-antineutrino annihilations. As a result, the X-ray flares following short GRBs are expected to be linearly polarized. The argument may also apply to the X-ray flares following long GRBs. Future observations with the upcoming Xray polarimeters will test this prediction.