Can X-ray emission powered by a spinning-down magnetar explain some gamma-ray burst light-curve features?

• DOI: 10.1111/j.1365-2966.2009.15538.x
• Publication Date: 2010-01-25T16:19:11Z
• Authors: N. Lyons; P. T. O'Brien; B. Zhang; R. Willingale; E. Troja; R. L. C. Starling
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); 0103 physical sciences; FOS: Physical sciences; Astrophysics - High Energy Astrophysical Phenomena; 7. Clean energy; 01 natural sciences; 520

10 pages, 5 figures, accepted by MNRAS<br/>Long duration gamma-ray bursts (GRBs) are thought to be produced by the core-collapse of a rapidly-rotating massive star. This event generates a highly relativistic jet and prompt gamma-ray and X-ray emission arises from internal shocks in the jet or magnetised outflows. If the stellar core does not immediately collapse to a black hole, it may form an unstable, highly magnetised millisecond pulsar, or magnetar. As it spins down, the magnetar would inject energy into the jet causing a distinctive bump in the GRB light curve where the emission becomes fairly constant followed by a steep decay when the magnetar collapses. We assume that the collapse of a massive star to a magnetar can launch the initial jet. By automatically fitting the X-ray lightcurves of all GRBs observed by the Swift satellite we identified a subset of bursts which have a feature in their light curves which we call an internal plateau -- unusually constant emission followed by a steep decay -- which may be powered by a magnetar. We use the duration and luminosity of this internal plateau to place limits on the magnetar spin period and magnetic field strength and find that they are consistent with the most extreme predicted values for magnetars.<br/>