The Escape Of] MeV Photons from Cosmological Gamma-ray Bursts PDF Download

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Languages : en
Pages : 11

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Book Description
The recent BATSE result indicates that gamma-ray bursts may be at cosmological distances. AS such one must reconcile the high photon densities with the observations of spectra to energies well above the pair production threshold. We have investigated two models of relativistic flows that could provide the requiste beaming to allow the escape of 100 MeV photons: a stationary relativistic wind with a photosphere and a relativistic expanding shell. For typical cosmological gamma-ray burst parameters, the expanding shell model requires a Lorentz factor ([gamma]) of only 102 compared with 3 × 102 to 103 for the relativistic wind. For the expanding shell model, events separated in time at the central source produce peaks observed to be separated by the same time. However, the shape and duration of the peaks are determined by the expansion. The expansion can occur over a much longer time (by [gamma]2) then the duration that the observer sees so gamma-ray burst could be larger than 102 light-seconds. We have made two crucial assumptions need require further study. The spectrum has been assumed to a be a power law and a two component power law or a power law with a high-energy cut-off would decrease the required [gamma]. The expanding shell model uses a infinitely thin emitting surface and one with a finite thickness could increase the required [gamma].