Metzger 2007 Short GRB from Proto-Magnetar spin-down

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arXiv:0712.1233 [ps, pdf, other]

Title: Short Duration Gamma-Ray Bursts with Extended Emission from Proto-Magnetar Spin-Down

Authors: B.D. Metzger, E. Quataert, T.A. Thompson

Comments: 5 pages, 2 figures; submitted to MNRAS Letters

Subjects: Astrophysics (astro-ph)

Evidence is growing for a class of gamma-ray bursts (GRBs) characterized by an initial ~0.1-1 s spike of hard radiation followed, after a ~10 s lull in emission, by a softer period of extended emission lasting ~10-100 s. In a few well-studied cases, these ``short GRBs with extended emission'' show no evidence for a bright associated supernova (SN). We propose that these events are produced by the formation and early evolution of a highly magnetized, rapidly rotating neutron star (a ``proto-magnetar'') which is formed from the accretion-induced collapse (AIC) of a white dwarf (WD), the merger and collapse of a WD-WD binary, or, perhaps, the merger of a double neutron star binary. The initial emission spike is powered by accretion onto the proto-magnetar from a small disk that is formed during the AIC or merger event. The extended emission is produced by a relativistic wind that extracts the rotational energy of the proto-magnetar on a timescale ~10-100 s. The ~10 s delay between the prompt and extended emission is the time required for the newly-formed proto-magnetar to cool sufficiently that the neutrino-heated wind from its surface becomes ultra-relativistic. Because a proto-magnetar ejects little or no Ni56 (<>