Two X-Ray Plateaus of Gamma-Ray Bursts: Energy Injection from Nascent Magnetars with an Evolving Magnetic Inclination Angle

Abstract As the central engine of gamma-ray bursts (GRBs), a nascent magnetar can release its rotational energy by magnetic dipole radiation. This is injected into outflow GRB jet. With rapid evolution inclination angle, perpendicular component magnetar’s surface field decreases rapidly. The loss rate characterized two different timescales. peculiar two-stage injection model will affect shape X-ray afterglow light curve. It shown that new shallow decay phase emerge following initial phase. result, there could be plateaus in effects various physical parameters on curves are studied detail. found observed afterglows 161217A and 190114A, both having curve, well fitted our framework.