Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21530303t&link_type=abstract
American Astronomical Society, AAS Meeting #215, #303.03; Bulletin of the American Astronomical Society, Vol. 42, p.300
Astronomy and Astrophysics
Astronomy
Scientific paper
Long-duration gamma-ray bursts (GRBs) occur when the core of a progenitor star collapses, forms a magnetized rotating compact object and powers a pair of magnetized relativistic jets. These jets emerge from the star with Lorentz factors gamma of a few hundred and opening angles theta 0.05 radians. Achromatic breaks in the GRB afterglow light curves indicate that the product gamma theta 20. However, magnetohydrodynamic (MHD) simulations of collimated jets generally give gamma theta < 1, indicating a conflict between these models and observations. In this talk we present a new class of MHD jet simulations in which the simulated jet is confined by a GRB progenitor star, modeled as a rigid confining wall that extends out to a certain radius. Beyond this radius, the jet becomes deconfined. We find that the onset of deconfinement outside the star causes a burst of acceleration with negligible change in the opening angle. In our fiducial model with a stellar radius equal to 104.5 times that of the central compact object, the jet achieves an asymptotic gamma 500 far outside the star and an asymptotic theta 0.04 rad, giving gamma theta 20. These values are consistent with observations of typical long-duration GRBs and explain the occurrence of jet breaks within the context of MHD jets.
McKinney Jonathan C.
Narayan Ramesh
Tchekhovskoy Alexander
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