Soft X-ray flares were detected to follow two recent short gamma-ray bursts, GRB 050709 and GRB 050724. These flares are likely due to the late time activity of the central engine. We argue that if short GRBs are generated through compact star mergers (e.g. NS-NS or NS-BH), 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 annihilation. 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 X-ray polarimeters will test this prediction.
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