High-energy emission in short GRBs and the role of magnetar central engines

¹ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
² Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK

Abstract

A significant number of long Gamma-ray Bursts (GRBs) detected by the Swift Satellite have a plateau phase signifying ongoing energy injection. Using BAT and XRT observations, we find that many short GRBs show similar behavior which challenges the typical short GRB progenitor model. We suggest the remnant of neutron star - neutron star mergers may not collapse immediately to a black hole (or even collapse at all) forming instead a magnetar. This model predicts that there would be a plateau phase in the X-ray lightcurve followed by a shallow decay phase, if it is a stable magnetar, or a steep decay if the magnetar collapses to a black hole within a few hundred seconds. By fitting this model to all short GRB BAT-XRT lightcurves, we show that a magnetar could power the observed energy injection. This model can be tested using the next generation gravitational wave observatories.