Curvature effects in gamma ray burst colliding shells
Mar, 200412 pages
Published in:
- Astrophys.J. 614 (2004) 284-292
e-Print:
- astro-ph/0403508 [astro-ph]
DOI:
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Abstract: (arXiv)
An elementary kinematic model for emission produced by relativistic spherical colliding shells is studied. The case of a uniform blast-wave shell with jet opening angle is considered, where is the Lorentz factor of the emitting shell. The shell, with comoving width , is assumed to be illuminated for a comoving time and to radiate a broken power-law spectrum peaking at comoving photon energy \e_{pk,0}^{\prime}. Synthetic GRB pulses are calculated, and the relation between energy flux and internal comoving energy density is quantified. Curvature effects dictate that the measured flux at the measured peak photon energy \e_{pk} is proportional to \e^3_{pk} in the declining phase of a GRB pulse. Possible reasons for discrepancy with observations are discussed, including adiabatic and radiative cooling processes that extend the decay timescale, a nonuniform jet, or the formation of pulses by external shock processes. A prediction of a correlation between prompt emission properties and times of the optical afterglow beaming breaks is made for a cooling model, which can be tested with Swift.Note:
- 13 pages, 5 figures, added back-of-envelope estimate of curvature relation, minor corrections, ApJ, in press, v. 614, 10 Oct 2004
- gamma rays: bursts
- gamma rays: theory
- radiation mechanisms: nonthermal
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