X-ray plateaus followed by sharp drops in GRBs 060413, 060522, 060607A and 080330: Further evidences for central engine afterglow from gamma-ray bursts

The X-ray afterglows of GRBs 060413, 060522, 060607A and 080330 are characterized by a plateau followed by a very sharp drop. The plateau could be explained within the framework of the external forward shock model but the sharp drop can not. We interpret the plateau as the afterglows of magnetized central engines, plausibly magnetars. In this model, the X-ray afterglows are powered by the internal magnetic energy dissipation and the sudden drop is caused by the collapse of the magnetar. Accordingly, the X-ray plateau photons should have a high linear polarization, which can be tested by future X-ray polarimetry. (research papers)