THE MILLISECOND MAGNETAR CENTRAL ENGINE IN SHORT GRBs
By Houjun Lü, Bing Zhang, W. Lei, Ye Li, P. Lasky. 2015
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One favored progenitor model for short duration gamma-ray bursts (GRBs) is the coalescence of two neutron stars (NS–NS). One possible outcome of such a merger would be a rapidly spinning, strongly magnetized neutron star (known as a millisecond magnetar). These magnetars may be “supra-massive,” implying that they would collapse to black holes after losing centrifugal support due to magnetic dipole spin down. By systematically analyzing the Burst Alert Telescope (BAT)-XRT light curves of all short GRBs detected by Swift, we test how consistent the data are with this central engine model of short GRBs. We find that the so-called “extended emission” feature observed with BAT in some short GRBs is fundamentally the same component as the “internal X-ray plateau” observed in many short GRBs, which is defined as a plateau in the light curve followed by a very rapid decay. Based on how likely a short GRB is to host a magnetar, we characterize the entire Swift short GRB sample into three categories: the “internal plateau” sample, the “external plateau” sample, and the “no plateau” sample. Based on the dipole spin-down model, we derive the physical parameters of the putative magnetars and check whether these parameters are consistent with expectations from the magnetar central engine model. The derived magnetar surface magnetic field B p ?> and the initial spin period P0 fall into a reasonable range. No GRBs in the internal plateau sample have a total energy exceeding the maximum energy budget of a millisecond magnetar. Assuming that the beginning of the rapid fall phase at the end of the internal plateau is the collapse time of a supra-massive magnetar to a black hole, and applying the measured mass distribution of NS–NS systems in our Galaxy, we constrain the neutron star equation of state (EOS). The data suggest that the NS EOS is close to the GM1 model, which has a maximum non-rotating NS mass of M TOV ∼ 2.37 M ⊙ ?> .
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/73512a4a867feccee1ab0933afb1fc32223d8d80
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In Astronomy and Astrophysics
Citations in the corpus
- Formation of Double Neutron Star Systems (2017, background): “…(102 − 105 s) X-ray activity in a large fraction of sGRB events, which is indicative of a continuous energy release from a central engine on timescales orders of magnitude larger than the typical torus accretion timescale (Rowlinson et al. 2010, 2013; Gompertz et al. 2013, 2014; Lü et al. 2015).”
- Neutrino-dominated accretion flows as the central engine of gamma-ray bursts (2017, background): “…by a hyperaccretion disk (e.g., Paczyński 1991; Narayan et al. 1992; MacFadyen & Woosley 1999) or a quickly rotating magnetar (or protomagnetar, e.g., Usov 1992; Dai & Lu 1998; Zhang & Mészáros 2001; Dai et al. 2006; Metzger et al. 2011; Lü & Zhang 2014; Lü et al. 2015; Li et al. 2016).”