X-ray flares raising upon magnetar plateau as an implication of a surrounding disk of newborn magnetized neutron star

The X-ray flares have usually been ascribed to long-lasting activities of the central engine of gamma-ray bursts(GRBs),e.g.,fallback accretion.The GRB X-ray plateaus,however,favor a millisecond magnetar central engine.The fallback accretion can be significantly suppressed due to the propeller effect of a magnetar.Therefore,if the propeller regime cannot resist the mass flow onto the surface of the magnetar efficiently,the X-ray flares raising upon the magnetar plateau would be expected.In this work,such peculiar cases are connected to the accretion process of the magnetars,and an implication for magnetar-disc structure is given.We investigate the repeated accretion process with multi-flare GRB 050730,and give a discussion for the accretion-induced variation of the magnetic field in GRB 111209 A.Two or more flares exhibit in the GRB 050730,060607 A and 140304 A;by adopting magnetar mass M=1.4 M_(⊙)and radius R=12 km,the average mass flow rates of the corresponding surrounding disk are 3.53×10^(-4)M_(⊙)s^(-1).4.23×10^(-4)M_(⊙)s^(-1),and 4.33×10^(-4)M_(⊙)s^(-1),and the corresponding average sizes of the magnetosphere are 5.01×10^(6)cm,6.45 x 10^(-6)cm,and 1.09×10^(-7)cm,respectively.A statistic analysis that contains eight GRBs within 12 flares shows that the total mass loading in single flare is~2×10^(-5)M_(⊙).In the lost mass of a disk,there are about 0.1%used to feed a collimated jet.