Extreme properties of GRB 061007: A highly energetic or a highly collimated burst?

Department of Physics and Astronomy, University of Denver, Denver, Colorado, United States
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 09/2007; 380(3):1041 - 1052. DOI: 10.1111/j.1365-2966.2007.12138.x


GRB 061007 was the brightest gamma-ray burst (GRB) to be detected by Swift and was accompanied by an exceptionally luminous afterglow that had a V-band magnitude <11.1 at 80 s after the prompt emission. From the start of the Swift observations the afterglow decayed as a power law with a slope of αX= 1.66 ± 0.01 in the X-ray and αopt= 1.64 ± 0.01 in the UV/optical, up to the point that it was no longer detected above background in the optical or X-ray bands.
The brightness of this GRB and the similarity in the decay rate of the X-ray, optical and γ-ray emission from 100 s after
the trigger distinguish this burst from others and present a challenge to the fireball model. The lack of a cooling or jet
break in the afterglow up to ∼105 s constrains any model that can produce the large luminosity observed in GRB 061007, which we found to require either an
excessively large kinetic energy or highly collimated outflow. Analysis of the multiwavelength spectral and high-resolution
temporal data taken with Swift suggests an early time jet break to be a more plausible scenario than a highly energetic GRB. This must have occurred within
80 s of the prompt emission, which places an upper limit on the jet opening angle of θj= 0.8°. Such a highly collimated outflow resolves the energy budget problem presented in a spherical emission model, reducing
the isotropic-equivalent energy of this burst to Ecorrγ= 1050 erg, consistent with other GRBs.

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Available from: Alice A. Breeveld, Dec 17, 2013
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    • "Reaching a peak magnitude < 11 (similar to 9th magnitude of GRB 990123), both the X-ray and optical lightcurves show single power law decaying behavior from the very beginning (∼ 80 s after the trigger). This suggests a strong external forward shock emission with enormous kinetic energy (Mundell et al. 2006) or a structured jet with very early jet break (Schady et al. 2006b). "
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