Exact versus Approximate Solutions in Gamma-Ray Burst Afterglows

We have recently obtained the exact analytic solutions for the relativistic equations relating the radial and time coordinates of a relativistic, thin uniform shell expanding in the interstellar medium in the fully radiative and fully adiabatic regimes. Here we reexamine the validity of the constant...

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Veröffentlicht in:The Astrophysical journal 2005-11, Vol.633 (1), p.L13-L16
Hauptverfasser: Bianco, Carlo Luciano, Ruffini, Remo
Format: Artikel
Sprache:eng
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Zusammenfassung:We have recently obtained the exact analytic solutions for the relativistic equations relating the radial and time coordinates of a relativistic, thin uniform shell expanding in the interstellar medium in the fully radiative and fully adiabatic regimes. Here we reexamine the validity of the constant-index power-law relation between the Lorentz gamma factor and its radial coordinate, which is usually adopted in the gamma-ray burst (GRB) literature on the grounds of an "ultrarelativistic" approximation. Such expressions are found to be mathematically correct but only approximately valid in a very limited range of physical and astrophysical parameters and in an asymptotic regime that is reached for a very short time only, if at all, and they are shown to be nonapplicable to GRBs.
ISSN:1538-4357
0004-637X
1538-4357
DOI:10.1086/498146