The Small-Scale Structure of Ultrarelativistic Blastwaves in Gamma-Ray Burst Afterglows

Details The Small-Scale Structure of Ultrarelativistic Blastwaves in Gamma-Ray Burst Afterglows The Small-Scale Structure of Ultrarelativistic Blastwaves in Gamma-Ray Burst Afterglows

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.1807m&link_type=abstract

American Astronomical Society, AAS Meeting #211, #18.07; Bulletin of the American Astronomical Society, Vol. 39, p.769

Astronomy and Astrophysics

Astronomy

Scientific paper

We review recent progress addressing the small-scale structure of relativistic blastwaves that are believed to occur in gamma-ray burst (GRB) afterglows. We focus on the role of cosmic ray acceleration and blastwave anisotropy in the evolution of the blastwave. The synchrotron emission in GRB afterglows suggests that a new, strong, and persistent magnetic field is present in the plasma that crosses the shock. Because cosmic rays accelerated in the blastwave cross into the shock upstream, they modify the structure of the blastwave and lead to in situ turbulent magnetic field amplification. Similarly, because conical segments of quasispherical ultrarelativistic blastwaves are causally disconnected on angular scales larger than the blastwave inverse Lorentz factor, the blastwaves can sustain initial anisotropy, imprinted by the process that drives the explosion, while they remain relativistic. Initial angular energy fluctuations in ultrarelativistic blastwaves imply a production of vorticity. In GRB afterglows, the number of vortical eddy turnovers as the shocked fluid crosses the blastwave shell is about unity for marginally nonlinear anisotropy. Thus the anisotropy must be nonlinear to explain the magnetic energy density inferred in measured GRB spectra.

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