Reverse shock emission driven by post-merger millisecond magnetar winds: Effects of the magnetization parameter

¹ School of Astronomy and Space Science, Nanjing University, 210093 Nanjing, PR China
e-mail: dzg@nju.edu.cn
² Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, 210093 Nanjing, PR China
³ Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing, PR China

Received: 4 January 2016
Accepted: 11 April 2016

Abstract

The study of short-duration gamma-ray bursts provides growing evidence that a good fraction of double neutron star mergers lead to the formation of stable millisecond magnetars. The launch of Poynting flux by the millisecond magnetars could leave distinct electromagnetic signatures that reveal the energy dissipation processes in the magnetar wind. In previous studies, we assume that the magnetar wind becomes completely lepton-dominated so that electrons/positrons in the magnetar wind are accelerated by a diffusive shock. However, theoretical modeling of pulsar wind nebulae shows that in many cases the magnetic field energy in the pulsar wind may be strong enough to suppress diffusive shock acceleration. In this paper, we investigate the reverse shock emission and the forward shock emission with an arbitrary magnetization parameter σ of a magnetar wind. We find that the reverse shock emission strongly depends on σ, and in particular that σ ~ 0.3 leads to the strongest reverse shock emission. Future observations would be helpful to diagnose the composition of the magnetar wind.