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GRB efficiency Revisited & Magnetar behind short GRB
Yizhong Fan (Racah Inst. Of Physics, Hebrew University of Jerusalem, Israel; Purple Mountain Observatory, China)
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Collaborators T. Piran (Hebrew University of Jerusalem, Israel)
D. Xu (University of Copenhagen, Denmark) Fan & Piran. 2006, MNRAS, 369, 197 Fan & Xu. 2006, MNRAS, submitted (astro-ph/ )
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GRB efficiency crisis? GRB efficiency is defined as
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Late internal shocks (Fan & Wei 2005;
Schematic features seen in early X-ray Afterglow (Zhang et al. 2006; Nousek et al. 2006) Late internal shocks (Fan & Wei 2005; Burrows et al. 2005) ? Pre-Swift GRBs GRB efficiency crisis! Energy injection
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To constrain with the late X-ray data
When the X-ray band is above the cooling frequency, the flux is only sensitively dependent on and (Kumar 2000; Freedman & Waxman 2001).
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Fan & Piran 2006
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Our result: Lloy-Ronning & Zhang 2004: Fan & Piran 2006:
Causes: In Lloy-Ronning & Zhang (2004): is too large to match the result of numerical calculation . 2. The inverse Compton effect has been ignored. Our result:
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No! (Fan & Piran 2006) The optical/X-ray afterglows of GRB 050401
De Pasquale et al Rykoff et al. 2005 Energy injection, as many authors suggested? No! (Fan & Piran 2006)
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A possible solution for GRB 060401 ( ):
But: What’s the underlying physics?
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The simple energy injection model has been challenged by more and more data (Panaitescu et al. 2006)!
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Is there a GRB efficiency crisis ?
The previous estimate on the GRB efficiency (with the late afterglow data) is overestimated. The energy injection model is not supported by the optical data.
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Magnetar behind short GRB?
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What’s formed in the double neutron star merger (theoretical speculation)?
Black hole (Eichler et al. 1989; Narayan et al. 1992)? Differentially rotating normal neutron star (Kluzniak & Ruderman 1998; Dai et al. 2006)? Magnetar (Rosswog et al. 2003; Gao & Fan 2006 ; Price & Rosswog 2006)? Temporary magnetar (Shibata et al. 2006) ? MHD Simulation
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Energy injection ? (Soderberg et al. 2006)
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Energy injection form: Constraint on the parameters:
A millisecond pulsar with dipole magnetic field Gauss is consistent with the data!
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With an energy injection from a magnetar Without energy injection
Fan & Xu (astro-ph/ )
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A very late/weak re-brightening.
Conclusion: The central engine of short GRB A may be a millisecond magnetar. Speculation: A very late/weak re-brightening.
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Thank you!
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