## Abstract

It is proposed that the gamma-ray burst (GRB) photons near the peak of the spectrum at several hundred keV are produced on very compact scales, where photon production is limited by blackbody effects and/or the requirement of energetic quanta (E > 2m_{e} c^{2}) for efficient further production. The fast variation of order milliseconds in the time profile is then a natural expectation, given the other observed GRB parameters. Analytic calculations are presented to show that the escape of nonthermal, energetic gamma rays can emerge within 1 s of the thermal photons from a gammasphere of below 10^{12} cm. The minimum asymptotic bulk Lorentz factor in this model is found to be of order several hundred if the photosphere is of order 3 × 10^{11} cm and greater for larger or smaller photospheric radii. It is suggested that prompt ultra-high-energy gamma rays might provide a new constraint on the asymptotic Lorentz factor of the outflow.

Original language | English |
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Pages (from-to) | 146-150 |

Number of pages | 5 |

Journal | Astrophysical Journal |

Volume | 529 |

Issue number | 1 PART 1 |

DOIs | |

State | Published - 20 Jan 2000 |

## Keywords

- BL Lacertae objects: general
- Gamma rays: bursts
- Radiation mechanisms: thermal

## ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science