Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008head...10.0505m&link_type=abstract
American Astronomical Society, HEAD meeting #10, #5.05
Astronomy and Astrophysics
Astronomy
Scientific paper
Evidence is growing for a class of gamma-ray bursts (GRBs) characterized by an initial spike hard radiation followed, after a 3-10 s lull in emission, by a softer period of extended emission lasting 10-100 s. These "short GRBs with extended emission" (SGRBEEs) show no evidence for an associated supernova (SN) and, in conflict with compact object merger models, appear to originate exclusively inside the disk of their host galaxies. We argue that SGRBEEs may instead be produced by the accretion-induced collapse (AIC) of a white dwarf (WD) or the merger and collapse of a WD-WD binary, perhaps thus sharing a close relation to the progenitors of Type Ia SNe. In this model, the initial spike of emission is powered by accretion onto the newly-formed proto-neutron star (PNS) from a small disk that is formed in the AIC or merger event. If the PNS is strongly magnetized (a "proto-magnetar"), the extended emission may be produced by a relativistic wind that extracts the PNS's rotational energy on a timescale 10-100 s. We have modeled the extended emission from GRB060614 using spin-down calculations of a cooling proto-magnetar, finding reasonable agreement with observations for a magnetar with a surface field strength B 3e15 G and initial rotation period 1 ms. The 3-10 s delay between the prompt and extended emission is naturally explained by this model as the time required for the proto-magnetar to cool sufficiently that its outflow becomes ultra-relativistic. In the case of WD-WD mergers, extended emission may also be produced by accretion of the disk formed during the merger prior to collapse. We discuss ways to test the AIC/WD-WD merger model for SGRBEEs and to distinguish spin-down and accretion-powered extended emission via late-time radio observations and by searching for off-axis events, which may appear as X-ray flashes with no associated SN.
Metzger Brian D.
Quataert Eliot
Thompson Todd A.
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