Unstable GRB Photospheres and Blueshifted e± Annihilation Lines

Kunihito Ioka, Kohta Murase, Kenji Toma, Shigehiro Nagataki, Takashi Nakamura

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can reproduce the observed non-thermal spectra with high radiative efficiencies, >50%. Internal dissipation below a photosphere can create a radiation-dominated thermal fireball. If e± pairs outnumber protons, radiative acceleration of e± pairs drives the two-stream instabilities between pairs and protons, leading to the proton sedimentation in the accelerating pair frame. Pairs are continuously shock heated by proton clumps, scattering the thermal photons into the broken power-law shape, with the non-thermal energy that is comparable to the proton kinetic energy, consistent with observations. Pair photospheres become unstable around the radius of the progenitor star where strong thermalization occurs, if parameters satisfy the observed spectral (Yonetoku) relation. Pair annihilation lines are predicted above continua. A closure relation exists between pair annihilation lines and cutoffs, which could be verified by GLAST.

Original languageEnglish (US)
Title of host publicationGamma-Ray Bursts 2007 - Proceedings of the Santa Fe Conference
Number of pages4
StatePublished - Dec 1 2008
EventSanta Fe Conference on Gamma-Ray Bursts 2007, GRB 2007 - Santa Fe, NM, United States
Duration: Nov 5 2007Nov 9 2007


OtherSanta Fe Conference on Gamma-Ray Bursts 2007, GRB 2007
Country/TerritoryUnited States
CitySanta Fe, NM

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)


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